As mentioned in the Github discuission, I feel strongly that I'm not too precious about naming it... 
in-geoshape seems better than in-polygon. geoshape is already in the spec as a data type in the spec already. polygon isn't.
I'm not sold on the importance of searchability of a function name. I think people will search in the docs for examples and they'll find it that way.
I discussed with @yanokwa and he doesn't feel very strongly. Since no one else has expressed strong feelings, we're leaning towards sticking with geofence.