My hope is a Kurnoth Hunter/Orion hero with a combat focus. As for allegiance things, I suspect the Stormhosts will be the way forward for allegiance abilities so I would like to see the various Groves take on more distinct identities, like Winterleaf’s Dryad buffs do currently.
The largest single change I want to see is an update on the Wyldwoods, possibly a complete rework to bring the “feel” of the woods in line with the more recent scenery, particularly the Nurgle Gnarlmaws and the BoC Herdstones, though I don’t know what specifically would need to be done, but the old Citadel Woods models are the worst part of the army when it comes to talking to new players, telling a prospective Sylvaneth player that they will need to buy a bunch of old terrain models just to play their army sucks. It also makes the model range extremely reliant on their allegiance abilities, making things like Skirmish or the Living City rules obnoxiously difficult to get into.