UK channels broadcast as well as stream, so they will probably never have as many catch-up/on demand users in the UK as a streaming-only service.
People are still creatures of habit and have to fit TV around other things, most are probably not going to binge an entire series in a weekend as they probably won't have the time.
Things like news or soaps that run all year like East-bloody-Enders can't be dumped onto iPlayer.
Does this include Christmas specials? Will we be watching them in October?
If you dump everything onto iPlayer, when do you take it off? Or is this a way of turning the BBC into a subscription service?
Can I think of any more questions?