I second this!!!
I hope the OP can quit worrying...
In the video Jony is quite clear about the bands.
In my opinion, just as they kept the 30 pin around for a long time to encourage large 3rd party accessory support, I believe they will keep this exact mechanism in play as many iterations as possible, so if someone ends up with say... a dozen bands, they can use them for years and years with each of their new
Watch "main units". That's a GREAT way to get people further invested in your ecosystem! I personally, have looked at the side views many times imagining it the inevitable 50% as thick... & it appears to me that the band's will still work marvelously.