This thread is like my head all the time.
I wonder if the x3 duradin lines will get a combined battletome and maybe a few hero or elite units to bind them together as a single force? As was done with Orruks and aeldari in 40k. They all actually compliment each prher very well.
Otherwise I’d like to see an new monster based race for destruction, maybe fimir or big bugs or clockwork monsters run by mad humans.
I would love new kit dragons that can be built up to support any faction or realm. Very customiaable along the lines of the Gargants. Maybe one or two sizes?
However, I think AOS 3.0 will kick off with Orks getting a whole new line of models. I would love wyvern riders.
In terms of sigmarines, Sigmar really should open another set of chambers to defend Azyr after Excelsis falls and is renamed Gorkcelsis. To combat destruction he may choose ruination, maybe with lightning golems and mad stuff, or maybe the Covenant chamber. In my over fertile imagination, this is a chamber of Stormcast wannabees, who have signed up to fight and die on the promise of being reborn as proper sigmarines. Sigmar has no choice but to deploy this reserve when Belakor sabotages his Anvil and his realm is threatened. Releasing this would allow existing troop types to get a much needed buff as these guys become a low points alternative.
I suspect however a new range of human fully mortal troop models wouls have to wait until The Old World drops. I can imagine default fantasy infantry with sepereate shields, healms and weapons on faction specific accessory spruces. So the same infantry spruce but with diferent add ons for Empire, Kislev, Brettonia but also Shyish, Azyr Ghur etc.
This is a bit like the approach taken with Primaris and 30k marines.
Finally I want a new set of terrain and engines for sieges.