I don't think there's anything odd about it at all. It would help maximise seat usage which in turn may help foster a better atmosphere in the stadium (granted it doesn't address the early leavers situation). In any case, regardless of whether the ticket has been paid for or not, the club are entitled to impose whatever conditions they want when selling that ticket.
I don't think there's anything draconian about the idea of giving a supporter, say, up to 3 chances per season where they don't have to inform the club of their non-attendance. That's pretty lenient IMO. What's far more draconian is some of the other shit that's been going on such as the alleged targeting of vulnerable individuals by some Showsec stewards and City seemingly turning a blind eye when complaints have been raised about it.