Nikosandros
Golden Procrastinator
It has indeed been "coming soon" for a very long time. It also seems to me that it is supposed to be closer to classic, but streamlined.This has been coming for many years. I've been getting the Iron Crown Enterprises Director's Briefings since early 2013, and RMU was mentioned in the first of those, and was already a thing at that time - so that's 10+ years.
I don't know where it has landed between RM classic and RMSS, but suspect it is probably closer to the former.