I am missing the same opportunity. But I dont think abouf DNF caches, but all i havent found yet (DNF + havent seek yet)...We have a lot of caches around, and I have found most of them, so majority of notifications is useless.
1) challenge map is needed
2) what about accepted and archived challenge? Will be forever marked as accepted?
3) delete senceless challenges (hugging, kissing)