“They’re a rail above the payments rails”
I don’t think this is right. I think we are looking at two sets of payments rails that do not overlap (which is good, because we want the flexibility and resilience this affords). There will be transactions that run over the banking network rails and there will transactions that run over the internet. Banks (and customers) will use both of them.
I general, it’snot clear to me that consumers (or businesses) will know or care. You walk about of Waitrose, an R2P pops up on your phone, you OK it and the money vanishes from your bank account. Whether it goes via banking network push (instant payments), banking network pull (cards) or internet push (stablecoins) is of no interest to you, it is something that the banks and the merchants will negotiate and agree between themselves.