I have to say that I'm not so sure the rumoured iMac Pro will be competitive with the M1 Ultra Mac Studio, performance-wise. To my thinking, the iMac was aways intended as an "All-in-One" consumer machine and, in that sense, the iMac Pro was really a one-off idea (probably a stop-gap for frustrated users who couldn't afford the Mac Pro). Now the Mac Studio has filled that gap, so if there is an iMac Pro it will probably sit between the iMac and the Mac Studio. So the progression, performance-wise, would be iMac < iMac Pro < Mac Studio < Mac Pro. That makes sense to me. Not to mention the fact that the M1 Ultra Mac Studio has a pretty hefty cooling system, which doesn't really point toward an iMac instantiation, imho.

Just my 2¢.