While limiting this to 15 bits worth of AS numbers solves some problems, it also immediately removes much of the potential use from this proposal, as this way there is still no solution for people who want/need to multihome in IPv6 but don't have an AS number today.
I've targeted this solution for the biggest corporations, for which (IMHO) multiple addresses are a non-starter. Such corporations have AS numbers. Such corporations don't crop up from nowhere.
But if folks feel we should just allow everyone, one could just as well allow full 16 bits or even 32 bits. That would just lead to the exhaustion of AS numbers, though -- and folks would be worse off than before, as also small enterprises would get AS numbers for the "easy multihoming ticket".