One thing that I haven't seen brought up yet, so I toss it out there:
How does a Words-of-Power character deal with spontaneous substitution?
Say I'm a WoP Druid (yea, it's not covered yet, I know, but I'm musing). Can I swap out my prepared slots for Summon Nature's Ally spells? (Thus allowing me to summon multiple creatures at once - something ordinarily not possible for me.) Or can I hot-swap in any WoP spell I make up, so long as it contains the Servitor Word in it?
I see some balance implications here.