I am contractually obligated to lend my vote to any story involving witchery or hexcraft, so I have no choice but to offer my favor to Grimoire.
I mean, it helps that it actually sounds interesting, besides 
In seriousness, though, I don’t think you need to be worried about oversaturation; I actually think your idea sounds like a pretty refreshing take on the genre. From what I’ve seen, urban fantasy stories typically tend to be more…well…urban. The smaller-scale, more rural feel of Grimoire, by comparison, sounds refreshingly quaint.
That said, the changeling story is also a very interesting premise, so I’m gonna agree with @Eiwynn here—I’d love to see you tackle both projects, if you feel up to it.