Actually, this rumor has Sense, as Apple needs to push gaming on Metal, and it will attract developers to re-build current iOS games to macOS as its relatively cheap, with the upscale market which the imMP target, Apple also has market for a less expensive model for non-pros (or prosumers) which actually are more used to gaming, is a thing that could spread across all it's ecosystem (tvOS also is featured as a gaming platform).
Of course this is not a thing narcissist Apple purist could assimilate, neither assimilate Apple has evidently considering AMD CPUs.
Remember pre- Mac pro reveal leaks pointing Apple was developing two Mac Pro, one of such "Mac pro" with a single GPU and compact form factor.
I don't know if there is a trashcan re-boot, I would love this gaming Mac to be modular and compatible with imMP cartdriges, but this Mac if coming, needs a single powerful GPU and powerful CPU with no thermal corners, likely won't be modular this grants the trashcan a second chance, but who knows if it's just an scaled down imMP