First of all: Id like to see something unique to the Mortal Realms, not just a revival of the old models/look. I always prefered the completly new stuff to updated models (Fyreslayers, Kharadrons, Idoneth, the new Daughters stuff).
Now coming to units:
Id like to see a mixed close combat/missile unit as basic battleline option (showing off Aelf skill by mastering multiple weapons)
Flying heavy cav. Decorated knights (keeping with the Hysh aesthetic) riding flying feathered beasts (eagle-adjacent maybe?)
A unit of mages (its Teclis army afterall)