This is a product in search of a market. The performance differences between fully loaded regular imac and one of these for 99% of what people do will be negligible and in some cases the raw speed of the regular maxed imac will beat it. This is a very niche segment of the market for people doing high end rendering that need more than 4 cores and are willing to pay for it and don't care about upgrade ability. Aside from that, it makes no sense to me unless you just like to waste money. The rumored mac pro modular however is possibly a whole different ball game.
People who render have long gone to PCs or to cloud based services, as those are much more cost effective. Rendering is done on GPUs now and those get obsolete much quicker than CPUs. And as you can‘t upgrade those darn iMac „Pro“s, you‘re lost with a slow machine after a year or so.
I don‘t understand what the market for those should be.