I would like to see a series of alternative casting stat feats for various casting classes:
- allows a caster to use a different stat to determine some combination of DCs, spell access and bonus spell points.

For instance:
Lore-bound Music
Benefit: You may use your Intelligence modifier instead of your charisma modifier when determining the DCs of your bard spells (but not bonus spell points or spell access).

- can be enhanced within the spellsinger tree to also provide bonus spell points based on intelligence

Insightful Divinity
Benefit: You may use your Intelligence modifier instead of your wisdom modifier when determining the DCs of your cleric spells (but not bonus spell points or spell access).

- granted for free if you take Knowledge domain

Charismatic Divinity
Benefit: You may use your Charisma modifier instead of your wisdom modifier when determining the DCs of your cleric spells (but not bonus spell points or spell access).

I think feats like this would make TR'ing more FUN as you don't have to completely regear when switching between some casting classes and it would create more build diversity by opening up some niche builds.

Practised Spellcaster feat:
Prerequisite: Spellcraft 4 ranks
Your caster level for the chosen spellcasting class increases by 4. This benefit can't increase your caster level to higher than your Hit Dice or 20, before epic levels are applied, whichever is lower.

I'm sure that this feat as been suggested before and it could really take the sting out of what would otherwise be some really fun builds, especially for newer players.