What is the mechanism by which you resolve multiple challenges against an account? Do you always go with the challenge which was issued first?
The only failure mode I see is that you can effectively "bet" a small amount of bitcoin regularly that someone will lose access to their account (or stop checking in) to gain access to it.
The only failure mode I see is that you can effectively "bet" a small amount of bitcoin regularly that someone will lose access to their account (or stop checking in) to gain access to it.