Re: "as fast as the fastest PCs."
How many VMs can I run on one of these iPad Pros?
While I agree that you do have a point, how many people need to use lots of VMs? I suspect that people who really do need a lot of VMs are probably fairly flexible about their choice of host OS. Anyway, as I'm sure you're aware, VM performance is heavily I/O dependent and I think that's going to be the bottleneck here (along with the performance hit if you need other architectures). But could such a device be okay assuming it comes with a good SSH client to your VM park?
My biggest worry with all this is trying to force people to abandon local file systems. Yes, it's convenient if you do work with multiple devices that the relevant files are easily available on them all, but it's not worth the risk of them not being available because you have a shitty internet connection.