Spin Fate - theoretically possible but I can see that it'd be a little difficult to prevent spin "farming" as it were. Saying that, I do see a way to do it.
Resist Fate/Deny fate - loses most of its attraction as you can't choose exactly what to reroll in NWN. It'd have to be something you can turn on that would automatically reroll your next save.
Fickle Finger of Fate - you could make this force the target to reroll their next successful save, but apart from that... not really.
Spin Destiny - possible, but it'd be horrific to use and implement.
Luck to the Wind - much simpler than other things above.
Seal Fate - by the time you've implemented the rest, this should be straightforward.
Favoured One - it'd just be a modification of the stuff above.
All in all, it'd be so fiddly to play with that I'm not sure it's worth it. I find psionics bad enough, but this would be quite a lot worse.
As you say, it's an irony that the strongest feat is easiest. Maybe many will still choose this class even if it only contains this one feature
The fate point system is challenging. Several variables & a group of feats have to be implemented just like what was done in psionic system, and spinning from harmless or none-saving spells should be abandoned. Don't worry, I think the most common way should be gathering points from spells then using them simply in a Seal Fate
But by now I'm even not sure how to change wizard spell DC in PrC...
Rerolling... I hate them. I think it only works well in slow paper game but not in computer. Difficult both to implement and to use, I think maybe we can just change them into some saving throw bonus spells?
I still believe it'll be a great class. The special requirement is hard to meet in D&D but is nothing in NWN -- you can just take the class and make a story in brain
