I want two characters, with reasanoble explantions for their appearences. Ian and Dogmeat.
Hell Ian shot me in the back alot, but he'll be so grateful to get a minigun there's no way he'd do
it again.
Well, they're both dead, unless FO3 is exploring an alternate temporal thread. It would be great to have Dogmeat back somehow though. I suppose there was the robo-dog-hybrid technology in NCR... but that seems sort of cheesy and little-kid-Disney-ish if it's used to bring back a loved character, rather than making a dog into a badass killing machine.
As for including FO2 characters as party NPCs, that's often a dangerous element in games as it can seriously damage the atmosphere or believability of the sequel. It would just feel.. un-Fallout-ish if they joined the party again, wouldn't it? Including a few as non-party NPCs seems almost a given though, e.g. Tandi and Harold in FO2.
Harold was the logical choice in leading a community of ghouls. Tandi being a non party NPC was an important link in joining the old Shady sands believably with the new NCR, lending a sense of continuity. It could also be imporant for an NCR that would be trusting of the "Chosen One", especially because the plaque on the Vault Dweller statue implied that nobody believed he was actually from the vault.
Yeah, how would you know that the bone is Suliks? there's tons of tribals in the wastelands :p
Simply include another forensic reference to Sulik, his sister, or the Chosen One. Maybe the all important vault 13 canteen was given to aid him as he parted ways with the Chosen One and Sulik set out on the long journey home. Actually, that's a great idea, if I do say so myself.
Maybe he didn't make it home. Maybe he did, and now rests with the canteen in a tribal burial ground...
NPCs' children are an obvious choice for NPC continuity. Vic's daughter for one, then there's the multiple chances the PC had in FO2 to continue his/her genetic line. The farmer's daughter, Phyllis wanted to have real "relations", etc. If the PC had enough speech capability, there was actually quite a bit of conversaion with Phyllis about seeing the outside world, and about Vault City's reproduction being regulated. I think this makes Phyllis an excellent choice if the developers decided to include the Chosen One's progeny in FO3, which seems likely as this was the link between the first 2 games.