Yeah, I felt like Sarevok and Viconia were poorly executed. It felt similar to the way Faldorn was used in BG2 to me, as just another villain that had to be taken out. Jaheira I liked, but again, her recruitment being all delayed till the end of the second Act is pretty frustrating there. Also, there are so many ways for her to get killed before recruitment, or to just bail, and the same thing with Minsc. This felt similar to the way that a character like Yeslick, Eldoth, Quayle, Skie, Tiax or Alora was less likely to get used in BG1 because they didn't show up until much later, or sometimes they would party break or just kill someone without much warning. For the returning BG characters in BG3, only Jaheira and Minsc really had to be accounted for in terms of the new systems for Class, Abilities and such, since the other pair weren't recruitable/playable. For Minsc, I liked that they turned Boo into an actual animal companion that could be used, but it was hard to spec Minsc out from his base stats with sufficient STR for his character archetype while still being an effective Ranger. Like he's totally reliant on potions Giant Strength juice. Jaheira didn't feel like she got enough special whatevers to capture the Fighter part of her Fighter/Druid archetype. She has some special equipment, Belm, Staff of the Ram, and Khalid's Amulet, but not really a lot in the fighter direction there. To me it would have made sense to give them each a bonus "Hero of the Realms" Feat, to make them seem more seasoned and desirable to have tagging along. +2 Bonus ASI would have made them seem more legendary and that would probably have been enough to get something going.
Imoen I think would be particularly tough though, because under the new scheme she'd probably be better off as a Bard or a Bard multiclassed into Wizard, than as a Rogue/Wizard. Under a level cap with spellslots granted the way that they are, taking a couple levels in Bard is just way better mechanically than lvls in Rogue (Thief), if pairing with Wizard, since Bards are now full casters.
To me this also fits with Imoen's whole vibe a little better. For example as a lvl 1 Bard with the Urchin background she gets a bonus to Stealth and Sleight of hands for the thieving, but she'd also get some cantrips like Friends and Vicious Mockery which seems thematic for her. Like she's always trying to make friends, and then viciously mocking them in BG1 lol.
Dissanent Whispers also seems thematic for a BG2 style Imoen, together with spells like Longstrider, Healing Word, and Bardic Inspiration (which are all extremely useful for a support character) she's immediately a lot harder to just ditch. Later she can get Magical secrets even, or switch into Wizard or Sorcerer and you'd end up with a character that's more in line with the Thief/Mage of 2E for the power curve.
Just taking some potential Muliclass options and comparing them A lvl 1 Rogue, lvl 4 Wizard, you wouldn't gain a spellslot for that lvl in Rogue under 5e, so thats capping at lvl 2 spellslots.
A lvl 1 Bard, lvl 4 Wizard, you end up with a lvl 3 spellslot (since both classes are full casters) which is just a much stronger character overall in combat. For utility outside combat the +1d6 bonus to companion rolls from bardic inspiration and persuasion face type stuff just makes her seem immediately worth hanging around.
This shows the difference between the 2 combos under quick Bg3 translation. With Bard she's already Hasty and has like a Lightning bolt or a Fireball plus all that other stuff lol. Dipping Rogue instead, sure expertise makes stealing gold a little easier but the sneak attack compared to the firebire or being hasted while doing whatever, along with the longstride and just seems like a better choice mechanically for her.


A lvl 1 Bard, lvl 4 Sorcerer is probably even better since you don't have to work a second attribute as hard to get some more powerful arcane spells in the repetoire.
Or she could just be a Sorcerer with Sleight of Hands and such coming from the background. Since she had such a high Charisma in BG1/2 it fits the archetype there, sorta, also in BG2 we don't see her as a spellslinger until after Irenicus has been all experimenting on her.
Irenicus is all talking about "the untapped potential" and is a Sorcerer himself, so I could see a situation where Imoen is reimagined as a more sorcerous Mage with the powers coming from Bhaal or whatever. If Imoen read any of the Ability tomes in BG1 it would justify a bonus to ASI or some flavor feats to make a multiclass build more robust and seem sufficiently powerful. In 2E a Dual Class Thief 7/Mage 8 was just a much more powerful lvl 8+ character, than anything I could pull off in 5E at the same level.
If they make her a Rogue (Arcane Trickster) then I guess she can have her signature Magic Missile, like the wand she's given at the outset in BG1. This is probably the most straightforward I guess, but as quarter caster she's never going to be doing the sort of big magic she achieved in BG2 or Throne of Bhaal that way.
I think if she remains a Rogue/Wizard to match her Thief/Mage of BG2, then maybe they need to make it so she comes into the party already overlevelled by at least 1 lvl. So for example when she says "Heya it's me Imoen" if Charname is still at lvl 1, maybe she comes in at lvl 2 from the getgo one step ahead?
Or if Charname is lvl 3, she could be lvl 4, because then she's not lagging behind as hard as a multiclass Char, and just let her cap out slightly sooner? I don't know it's a tricky situation to navigate at the Friendly Arm Inn. I think a bonus feat would make sense for her, because feats are fun and they allow for creativity. The way they are awarded by default every 4 class levels is a pretty big nerf for Multi Class type, outside of certain Class combos that seem to already synergize well. Most of the old Multiclasses have already been spun off into their own unique class or subclass now, so it's just a lot to try and puzzle through. I think some other tricky multi Characters for BG1/2 would be Montaron, Coran, Tiax, Nalia, Jan Jansen for same reasons as Imoen.
A character like Branwen or Kivan or Ajantis would be a lot easier to translate, same deal for Heir Dalis, Keldorn and Valygar and such in BG2 since there are a lot of subclasses to cover their types. Aerie would be probably have to be Wizard mutlicassed into Cleric, since the reverse would offer a lot of weapons/armor options that don't really capture her vibe to me, but at least her spellslot progression would be on pace. Under the new scheme it just doesn't make a whole lot sense to me to pair a Full caster class, with a class that doesn't gain spellslots. Sneak Attack and the expertise bonus doesn't seem like enough when compared to a spellslot at the highest of the high end, especially if it costs a feat somewhere along the way.
I think it would be fascinating to see what they do, but I suspect they'll take a lot of liberties, which will likely give us cause to grumble lol