Let's begin with the HUGE sign as to why it is not Wallace or Weevil or anyone else but (possibly) Duncan and (totally) Logan at the door. We were told that the episode would have a love life cliffhanger -- at this point, ONLY Duncan and Logan would fit that scenario, so by that right, it HAS to be one of those two. Eliminating everyone else.
And Duncan doesn't fit. His dad was arrested; his mother no doubt needs him. If he really needed to see Veronica/talk to Veronica, he would have done so at the crime scene, or gone to the hospital or gotten there a lot earlier. At the point when she opened that door, he'd be dealing with the fall-out from Jake's covering up the murder. Police, press, Celeste, etc. Okay, so you ask: Why wouldn't Logan be dealing with the fall-out of Aaron committing the murder? Simple. Duncan loves his dad and is going to want to be there for him. Logan? His dad? Love? Not so much. Especially not now.
1. His dad was sleeping with a very recent ex.
2. His dad killed said very recent ex.
3. His dad covered up murder of said very recent ex.
4. His dad let him be arrested and sit under questioning instead of confessing.
5. His dad attempted to kill his most recent very recent ex.
Add to that, dad was (in his eyes) responsible for mom's death. Oh and then there's the little fact that dad beats him.
Again, Logan ain't gonna wanna be there for Aaron. While Duncan would want to be there for Jake. Which brings us back to Duncan. Aside from the logistics, again, love cliffhanger, and his and Veronica's scenes just didn't contain any romantic vibe. There were two line readings (gotta give props to Kristen) in the scene after the Aaron/Lilly death scene that bespoke to me where Veronica's feelings lie. The first was when she was explaining that Aaron beat up Trina's boyfriend and then she said, "He beats Logan, you know?" And the way she said that line, especially Logan's name, was filled with a quick burst of OHMYGOD!LOGAN!, that was quickly tamped down because now really wasn't the time. But it was there, this thread of oh my poor Logan, was totally in her tone of voice. So, girl has feelings for Logan. Big-time!
The second line was when she told Duncan that she wasn't his sister. I'm sure some may have read it as, 'see, we can be together!' But that was totally not the line reading. The line reading was, 'I know you're squicked out because you think you had sex with your sister, but I'm not your sister, so no worries. Gotta run!' with a cheery smile. So, girl does NOT have those feelings for Duncan.
But, but, but Logan was trying to kill himself, you say. He wouldn't be running off to Veronica, he's in the depths of despair. No, he wasn't. He wasn't attempting suicide; he was tempting fate. He didn't care if he lived or died in that moment, true, but that's not a suicidal thought. Suicide is WANTING to die. Logan didn't care either way. That's important. He wasn't that far gone.
Okay, so, Weevil was going to beat him up, you reason. Well, I'm not so sure of that. (Postulating here big-time, I admit.) It's very possible that Veronica tried to call Logan first (before she called Keith). After all, Logan is Aaron's son and he needed to be warned. She couldn't reach him, maybe she then called Weevil to find Logan, giving a quick sum-up of what's the deal. Then she calls her dad, then tries Logan again, no luck. We cut to Weevil showing up and, I'm sorry, but that look on his face, tone of his voice -- compare it to the way he spoke about "rich boys" at the beginning of the episode, totally not as menacing or enraged. In the final scene with Logan, he just sounded annoyed. If Weevil believed still at that point that Logan killed Lilly, would he sound only merely annoyed? I don't think so.
Alright then, why would Logan show up at Veronica's door? He totally can't forgive her. And to that I say, yes, he can. If Veronica had told him on the beach that she believed him and was crazy to think that he had killed Lilly, she was just confused and with finding out about his alibi being blown and everything, she was so sorry ... he would have so forgiven her right then and there. Completely. Would there still be issues? Of course. But he would have forgiven her. Why? Because Logan is filled with remorseful self-loathing; he believes that he isn't worthy of Veronica at this point. He lied to her about the alibi; just like he was the bad guy in giving Duncan the GHB, so HE screwed up and if Veronica forgives him for his bad, then he has another shot at salvation. I'm not saying that Veronica is going to "save him," just that in Logan's mind, she's a good that he's been denied. Logan's given her reasons to not trust him, to believe the worst of him and these are the consequences of his year-long descent into jackassery. We saw in how he forgave her for:
1. Standing him up without a word.
2. Ignoring him for a weekend.
3. Accusing him of rape.
4. Leaving him stranded cold again.
5. Avoiding and ignoring him for a few days again.
All in the space of a few days, maybe four or five, it's reasonable to assume that once again Logan would forgive her because he believes he brought it upon himself. Remember, he's a child of abuse and in many cases, the abused are led to believe that they are the ones to blame. So, it's his fault and if Veronica's forgives him, it is despite what a jackass he is.
And speaking of that good ole psychotic jackass rep ... many speculated that Logan would OPJ on her again and some are still speculating that he will. But I don't see how that is even a question now. She accused him of rape. He forgave her. She stood him up. He forgave her. She ditched him without a word. He forgave her. She accused him of murder, setting the cops on his (fine) ass and while he didn't forgive her -- he was on that road. Logan was EXPLAINING himself to Veronica when talking about Lilly. He wasn't raging at her, he wasn't snarking, being petty or mean or cruel or vicious or vindictive. Yes, he called her a "heartless bitch" but that was ripped out of him and was filled with pain; she broke his heart. And those words were not said in rage or in sarcastic taunting, they were spoken in a maelstrom of suffering and heartbreak.
Clearly, this guy is NOT going OPJ on her again. We already saw his reaction to her accusing him of murder. And it wasn't one of a pyschotic jackass, obligatory or otherwise.
So to recap: It's not Wallace because it's a love-related cliffhanger. Same goes for Weevil because no doors have been opened with either of the 'W' guys romantically. It's not Duncan because the feelings aren't there from her end and he'd be too tied up in dad's been arrested-related stuff. Which leaves Logan. Who has shown forgiveness for Veronica in the past. Who showed himself, more hurt than angry, on the beach. Who, most importantly, is once again all alone. The last time he was all alone -- when Lynn died -- he showed up at Veronica's door just about EXACTLY the same way that this final scene was shot. The difference is that this time we didn't see Logan standing outside, arms wrapped tight, giving himself the hug that no one else was there to give.
One final thing that points to Logan: Next season begins at the beginning of the school year. With a few judicious flashbacks, we can put Logan and Veronica to some degree of on-track. Yes, they have issues, but they were already laid out in this episode what those issues are and how they both deal with them. She runs away; he self-flagellates. They need to communicate. We get that; they get that. It's clear that these are the issues with what we've seen; not saying that they will easily master the dealing with of these issues, but they know the deal. If we were to see them getting through the early stages, there would just be long, meandering discussions discussing those things that we, the viewers, already know and that would resemble Dawson's Creek which is so not the VM style. That is not the case for Duncan/Veronica at this point. They'd have to start from the ground up and essentially do for Duncan/Veronica what they did for Logan/Veronica from The Wrath of Con to at least Weapons of Class Destruction. And we'd need to see that evolution, not have it inferred from a few flashbacks.
Furthermore, if they choose to go that route with VD and have them together at the beginning of next season, they have nowhere to go with them. Either (a) they work out and thus are pretty much left with no story on that end (and where is Logan gonna be?). Or (b) they don't work out, they break up early on and then that effectively closes the door on a potential VD hook-up in the future and they'd be crazy to completely shut that door now.
So. Totally Logan at the door.