The DM decided to allow the feat retraining after all.
I feel a little weird about it, but I figure my character will be using a weapon he can never really upgrade (damage increases slightly with caster level...), so I'm just going to go with the flow here and see what happens. I have no idea how the build is going to fare since character information isn't shared between players for RP reasons and I've never played under this DM before.
I have a reasonably high wisdom (22), which gets be some bonus slots, but at our starting level (level 7), it seems like managing what is still a very limited number of spell slots is going to be my biggest issue. The DM okayed swift haste for triggering swiftblade abilities, which allows me two castings of moon blade as my level 3 spells, but that leaves me with limited options for fueling arcane strike.
EDIT: Also, maybe some of can shed some light on this. If I hit someone 3 times in a round with a moonblade, say for 6 damage, 10 damage and 8 damage, what is the DC required for them to cast a spell next round? Is it the highest damage (10), the total damage (24), or would it require three individual checks (6, 10 and 8, respectively) to cast a single spell?