If miners were say 1 hour apart, you would get substantial forking going on, and although in theory the longest chain would eventually dominate, you might have to wait for quite a few more confirmations.
I have always thought that /that's/ where alternative currencies come in, this time with a real purpose rather than a me-too. There could be bitcoin, plutocoin, you-name-it.
At the edges, there could be a flourishing inter-currency trade.
agree with OP, bitcoin will fit perfectly for the purpose and we almost got the communications covered too with quantum physics of course