Could say M1 7 GPU == A14X and M1 8 GPU == A14Z going by the A12X/Z naming so not really outside Apples normal modus operandi except the 16GB ram. So I think the next IPhone will still get a new A15. I think It is more interesting what the rumored high end chips with 12, 16 etc. Cores Will be based on, A14 or A15.
Yep, the M1 in an iphone would throttle down to the point that it would perform worse than an A14 bionic, and use a lot more battery in the process. Right now the A14 bionic is overkill for iphones, heck even the A12 and A13 are not even remotely pushed to their limits.