Improved Combat Casting for all full casters in epics
Give all full casters (Wizards, Sorcerers, Warlocks, Clerics, Shamans, Favoured Souls, Druids) Improved Combat Casting at level 21 (level 11 for Palemasters).
Right now every caster in the game has to activate defensive casting manually. There is no reason not to do this once you have enough concentration, since it becomes impossible to fail the skill check. However it's still super annoying to activate it everytime and easy to forget. It's also not obvious to all new players that this is even an option (I went through several characters before realizing it was myself).
It's no balance concern either since all of the classes above absolutely need concentration (they can still be hit while casting and thus lose their spell, which is quite bad), so it's not like this would allow them to skimp on a skill.
It would just be a massive QoL increase with no downside.