It wojuld make most sense for Canon to take the follwing 3 steps
1) expand EOS M system
* after M5 quickly bring strong updates to M10 and M3 ... both compatible with external DC-EVF2 ... that would please the "as small as possible" and "take it along as a backup crop body" crowd.
* add a select few EF-M lenses in line with current lineup: optically as good as 22/2.0 and 28/2.8, compact and very affordable. Especially a compact EF-M 85/2.4 IS STM.

And a 50/1.8 IS. That might make the "we need more EF-M lenses" whiners happy. It would certainly make me happy. Smart, Canon!
2) Announce discontinuation of Rebel DSLRs and EF-S lenses and swithc to mirrorless crop sensor cameras only
* bring one last round of updates, namely an SL-2 and a 760 successor, and announce, "that was it, no more after this, but EF-S lenses will remain fully functional with adapater on EOS M bodies".
3) Introduce FF MILC system in a smart way
* bring a 3-pack of A7/R/S II competitors.
** call one EOS X1. Include full-blown 4k video, to keep the "4k video whiners" at bay. Include kick-ass AF-system, and fps, to keep the wannabe-wildlife and sports-shooters in forums happy. Make it big and fat to include a huge heat sink and a big battery in a big handgrip. That makes the "my hands are Trump-sized" crowd happy. Put a bolted-on EF-adapter-nozzle up front to make the "no adapter ever"-whiners happy. And make it very expensive (say 8 grand) ... all those folks should have to cough up some serious dough.
** call one X3 and make it hi-rez sensor, medium size and with an EF-nozzle up front. That should please the landscape and it's giotta have EF-mount crowd.
** call one X% and make it as small as possible with EF-X mount. Bring a select few good, small and affordable EX-F primes ... 24/2.8, 35/2.0, 50/1.8, 85/2.4 IS and compact, collapsible versions of 24-70/4 and 16-35/4 IS zooms. Include EF-X/EF adapter "for free".
Tell the world that for the time being, DSLRs will continue to be built, but 1 series only.
And updated EF-lenses also, but L-tele/supertele/Tilt-Shift only.
See what sells in what quantities ... and adjust strategy accordingly.