Though I doubt it will happen, I'd love to see:
- A general reduction in cooldown times for defensive abilities (or at least for skills like Tempered Will and Bulwark).
- Making it all feel a bit more cohesive; e.g. Paladins got some nice new tools (and changes) in 4.0, but a lot of them (especially the gauge) feel rather disjointed and / or tacked on.
- A re-working of the cross-role abilities to provide some actual choice (as opposed the numerous 'must-have' and 'mostly-unless' abilities we current have).