I'm fine with most main NPCs as they are right now, although I'd love a bit more about Urianger! And I would not mind if we'd let Tataru behind in Kugane for 5.0

It's true that the twins have most of the spotlight, but their writing is overall excellent. I like how they fullfil different functions for the WoL, and how they are more complementary to each other than just a duo of characters with the same identity and purpose. I also like how we get "breaks" with them, Alisaie being away for most of HW, and Alphinaud now stepping a bit back from the WoL.
I'd love it if 5.0 consisted on WoL/D and Alisaie trying to get Alphinaud back from whatever could happen to him until then.

What I would like to avoid is getting a "NPC from there" leading 5.0 MSQ (namely what we got with Lyse). It was ok for Stormblood, but I don't want for instance Cid as a main MSQ buddy for 5.0 if we go to Garlemald for instance. I prefer the outcast/lonely feeling we had in Heavensward. But it's just a matter of taste I guess