You will NOT be able to swap for the 8700 but you WILL be able to swap for the 7700 with no issues what so ever, literally on boot-up the system will immediately recognize the new CPU. The 8700 is a 6 core chip and they don't have any EFI to support that with the current OS. The iMac Pro doesn't even use the new Coffee Lake chip, so it may be doable in the future, but not as of yet. BTW, the latest iMac Pro uses Xeon chips for multi-threading and a kick-ass GPU, so that one will be upgradeable in the future. Hopefully, Apple will come up with some OS updates and the new 8th gen Intel chips will benefit.