This RK Scale locomotive thing is not a new thing at all; it's been around for several years.
It's a great idea, especially for those of us to whom extreme and often delicate
detailing means little, so far as the essential -image- of the prototype is present.
Unfortunately for those of us who are mostly about steam the RK Scale group is a
diesel show, almost entirely. I can understand this, actually.
Almost? Though I do not believe that they were ever marketed as "RK Scale", both the
MTH USRA 0-8-0 and the low-end version of their USRA 0-6-0 were/are both full
O-scale items. These are, of course, small or small-ish locos, and can take very
sharp curves. The RK 0-6-0 is not the same tooling as the true Premier version of the
0-6-0, and the 0-8-0, while a nice model, is simplified in its detailing.