I think developers flocked to Intel Macs because it gave them one machine that could run Mac, Linux, Windows in virtual or bootcamp environments. If x86 compatibility goes away, developers may jump ship to Linux or Windows machines.
I used to have a PPC G5 iMac running Linux. It was fine; hitched me onto the Linux-on-Mac train for more than a decade once I finally ditched Mac OS X. And Linux already works nicely on ARM - it's the most common deployment.
This may be a terrible outcome for multi-OS users, but it's not guaranteed.
