Over the past decade, big manufacturing corporations have learned to calculate product flows with amazing accuracy. If Canon has been planning the move to RF for some time now, and they have a timeline for tapering off EF production, how overstocked do you think warehouses, distribution centers, and retail shops are at this point? How overstocked do you think they will be a year from now?
I do think Canon will put out one more generation of a few compelling EOS bodies, in part to give RF time to gear up, and in part to drain down EF inventory. EF has to remain relevant for a period of time.
I also think they have enough savvy, experience, and brute computing power to not get caught with mountains of unsold lenses.
So, "if" might seem silly to you, but, please, share some insights. Is Canon overstocked? Do they have decades of new, unsold lenses? Years? How many that match the typical 7D series wish list of new lenses? How long will Canon keep cranking out more L series EF lenses?
Used lenses, on the other hand, who can say?
EF-S will probably outlive EF by quite some time. In fact, maybe the low cost Rebels will remain what the great majority of Canon customers buy.
RF will take considerable time to displace EF completely. But there is a psychological component. For example, Toyota is selling 2018 RAV4's at or below cost right now, as the 2019 version is a reboot. Dealerships don't want the old ones around when the new ones fill the showrooms. Am I the only photographer holding off buying more EF lenses with a thought toward whether a better native RF version might be coming along?
There is great opportunity ahead for bargains on legacy EF lenses, and many photographers will take advantage. Just last week, new ef 50mm f/1.2L's were on sale for only $1069 USD from authorized dealers. And RF was just introduced!
(Is a new ef 50mm f/1.xL coming? Asked in another thread, I know, but what do you think?)
Perhaps you think a mirrorless body cannot be built that seriously challenges dSLR's for fast action. If so, you aren't alone, and that type of photography might sustain EF longer than expected.
Please, reveal the future in your crystal ball. But be careful. This is a sensitive topic. Discussing the value of EF lenses in a collection is scary!