Promise me something, *anything* that I can do with the new conversion and could not do with TUTU4, and I am going to change my mind. Playing BG2, dragging zombie-NPCs into BG2 from BG1, or a prespective of working for another few years on more BG1NPC to BG2 mods, or playing CtoB/TDD/SoS/NEJ and similar mods aren't my idea of fun. BG2 is done for, as far as I am concerned.
Well, if you'll stop playing BG as soon as Sarevok falls, BGT or BGTUTU can offer nothing more (but nothing less either) than TUTU. For others however it would be much easier to have a single platform on which all BG1 mods work.
If you will continue: BGT basically offers a sense of continuity to the game in the sense that it adds a transition and the NPCs in BG2 who also appeared in BG1, keep their stats (and any changes you made to them) from BG1. Also NPCs you killed during BG1 won't reapper (Minsc won't be in his cell f.e.) That's basically all, I think. Not that much maybe, but if it can be done (and has been done) why not?
On the zombie-NPCs. I never liked these either - NPCs without BG2 content should not reappear unless they have as much content as a normal BG2 NPC. I don't know if Ascension removed them from his latest BGT version, kicked them out of the party right before transitioning to BG2 before.
Also, who forces YOU to make the BG1NPC to BG2 mods - I know you made Kivan, Vlad wants to reintroduce Shar-teel, Seifer is working on a mod in which Ajantis reappears... Ideally, these authors should take into account whether these characters were part of a BG1-romance or not but that's maybe asking for a bit too much.
With Ascension's Mequel the feeling of continuity should become much stronger - explaining why characters leave, where they go to, what the PC does in between the death of Sarevok and the capture... And I know he will take all BG1NPC and all mods on BG1NPC to BG2 mods into account.
It's just that, without the compatibility, this new project will never be a 'merge' - since many BGT players will stick to the old BGT. Of course it is possible the merge might never be a succes in the first place and will divide the community even further, as you seem to believe. I hope it will not though.
Hey, and you know why this place is called Spellhold, don't you? This is the place for those criminally insane due to an excessive obsession with compatibility.