Casting in Shapechange/Polymorph...is possible! What?!?

[Sun Wukong]

Pretty much, the issue here is: if Natural Spell exists, why not have an Arcane Magic Form equivalent? If the Corebook background for Polymorphing isn't enough, then yes, put in a "sacrifice" of a Feat Slot.

Automatic: Still spell. Automatic: Silent Spell. That is 8 feats in total, 6 of which need to be taken in the epics. You could make do with Just Automatic: Still Spell feats and using Silent spell when necessary though, so the cost would be down to 5 feats.