Well, we know that AMD's chips - which use the next largest TSMC node compared to Apple's - have a lot of diminishing returns from increasing the available power envelope above M1-like ultraportable levels, at least in the kinds of core counts you typically find in consumer desktops. So it's possible that even if Apple did ship a full desktop chip in a system with proper cooling, it wouldn't be that much faster. (It's also likely that they just won't bother, Apple being Apple.)