WKT is certainly not out of the realm of possibility for ODK Collect, just AFAIK its not a current supported feature and there's nothing currently in the development pipeline to add it. But if the likes of GeoODK already supports it then perhaps there's some existing code we could pull in... And I see there's already been previous discussion around this, here, so perhaps followup in that thread and see if you can get more traction on turning it into a reality!