My guess is that they'd still keep the efficiency cores around, but provide more performance cores. So likely a 12 or 16 core processor, with 4 or 6 of those dedicated to efficiency cores.

The M1 supposedly has a 10w TDP (at least in the MBA; it may be speced higher in the MBP13). If that's the case, there's a ton of power envelope headroom to scale to more cores, given the i9 9980HK in the current MBP16 is speced at 45 watts.

I'm very scared of this architecture once it gets up to Mac Pro levels of power envelope. If it doesn't scale, then it doesn't scale, but assuming it does this is so far beyond Xeon/Zen 3 performance it'd be unfair to even compare them.

This is the effect of focusing first on efficiency, not raw power. Intel and AMD never did this; its why they lost horribly in mobile. Their bread and butter is desktops and servers, where it doesn't matter. But, long term, it does; higher efficiency means you can pack more transistors into the same die without melting them. And its far easier to scale a 10 watt chip up to use 50 watts than it is to do the opposite.