As for leaving extend out I feel that is really bad since a bard does not get a lot of extra feats to play with anyway. But if thats the case then I hope when you start planning the enhancement subclasses for sorcs and mages that they are held to the same requirement difficulty as bards were. Warchanter= str 13 base then power attack and weapon focus
Spellsinger= Most metamagic feats except extend(because it is common)

So given that we were held to those types of prereqs I hope mages will have similar requirements such as maybe combat casting as a have to take feat and maximize/heighten are not on the lists.