Cinema cameras aside, why?
Who want's this over full-frame? With today's processors, FF has proven to be just as performant as something like the 7D line. If you give me the "reach" argument, then I would give you the FF crop argument. If you give me the cost argument, then I point to the RP. Cheaper than that then you're going to have an up-hill battle against Fujifilm and Sony, or you know, Canon's M lineup.
I don't think it makes any sense, but maybe that's just me. I just hope they don't split their attention developing 'RF-S' lenses that are inferior in every way.
The only way it would be remotely interesting to me is if they made a really good, significantly more compact camera body with some really good, compact, L-glass (IE, competitive with Fuji's lenses), while also obviously maintaining the ability to use FF lenses. Then, maybe I'd justify one as a travel camera/backup body.
But seeing as how they never made L-glass for EF-S...
In other words, give me an RF line of APS-C lenses that can go toe-to-toe with Fuji X or GTFO.