In addition to my 5 year prediction of where this is headed, a couple big factors in all of this are:
A) If Canon just makes the same lenses as today with just RF mounts, then this move will take more time. Those that shoot macros, sports, and wildlife are pretty happy with the lens selections today, and just like it took a while for people to gravitate toward MKII and MKIII of EF lenses, that same mentality will exist with RF. People didn't move in droves to the newer lenses, MANY today still shoot with the originals.
B) If Canon makes unique lenses like the 28-70 f2, and other lenses that either they don't have today, even if competitors have made them, then the move to RF willo occur faster. If they make a 50-150 f2 for example, or some faster lenses with IS that don't have IS today, etc, then this progression to mirrorless just to gain access to these lenses will move faster. Better RF replacements for lenses that aren't particularly sharp in certain cases, lenses that aren't very fast for AF or are known to have AF issues, and lenses that aren't built all that great will matter here too.
C) Body-wise Canon HAS to introduce IBIS, they have to have blazingly fast and accurate eye AF during continuous focus priority shooting, definitely more resolution, faster burst, better 4K implementation, more customization, and they have to STOP doing that stupid "we will turn on/off inconsequential features to differentiate our models", and do something more substantial. This latter behavior worked ten years ago with the 40D/50D vs Rebels and then the 7D, but those days are over.
If you shoot macro today, the lenses today are great. If you shoot portraiture, there are so many options, and you don't need sharper lenses, because you invariably touch up or soften the skin now anyways. If you shoot sports, it would be nice to have different zooms that are faster, so if they follow b) and they make a capable sports camera, then EOS R/RF will be a great option, if neither of these happen, sports shooters won't move over quickly. Landscape shooters won't move over until they have greater resolution mirrorless (people are really attached to their 5Ds/r and A73r bodies). Wildlife shooters will move if the reach and sharpness is there.
So many things have to align for people to move "in droves" to the new mirrorless branding and RF lenses. When you have so many factors, some dependent on Canon, and the rest dependent on the millions of photographers, there is no way DSLR and EF/EFS/EFM lenses are going away in the next couple of years. This is going to be a long ride.
Those with GAS, those with older gear that have skipped the latest few releases, those that are diehard Canon lenses only and don't open themselves up to great 3rd party options, those that gauge everything photographic around sharpness at the pixel level, and those that aren't using their current gear to its fullest capacity because either their gear, or they themself, is lacking are the ones that will be the early adopters, those that are happy with results today and are more conservative will progress more slowly through the new mirrorless and mount landscape.
For those that want mirrorless for a weight and size savings, well forget that for now, because either the EOS-R now or the current RF lenses really get them to that goal.
BASIS FOR OPINION
Just my opinion, but I have been on a few boards for nearly 2 decades now, and my assessment was developed watching both those oldtimers on the boards and how they have moved through releases, along with new members asking questions and buying up gear. I have also watched Sony through these years and when the MKIII bodies came out, Sony hit enough of a home run to pull away die hard Canon shooters. Canon isn't at that level yet. Give them 2-3 more releases going into 2020, and that might change a bit. However quite a bit of damage has already been made, and Sony will keep churning out better bodies, so again this will play a part.