Multi-sig transactions and/or two-factor authentication can remove most of the risk of a 'Bitcoin card' ... so that the irreversibility is not a problem, except in an infinitesimally small number of cases, an acceptable level of risk.
I haven't taken multisig into account, just two factor. That's mostly because it's a new concept I'm not sure I fully understand. Is there a really good explanation of how that would work in the Bitcoin system? It might be I could incorporate it into this design, or rework the whole concept to leverage it properly.