[Symmetry]

The number of transistors sure. The engineer time to design new features that don't interfere with old features is high. The verification time to make sure every combination of features plays sensibly together is extremely high. To the extent that Intel and AMD are limited by the costs of employing and organizing large numbers of engineers it's a big deal. Though that's also the reason they'll never make a second, simplified, core.

[failwhaleshark]

It's never going to happen. The ISA is a hardware contract.

[PopePompus]

When things get to the point where AMD is considering making nonmaskable interrupts maskable (as the article states), maybe it's time to invoke "force majeure".