It's easy to say, "M lenses haven't poached EF-S lenses; therefore, RF lenses won't affect sales of EF lenses." But this is not based on facts; it's conjecture.
It is true that when it comes time to buy a new body for certain purposes I may buy an RF over EF.
What is conjecture is the extent the sales will be impacted, either positively, negatively or any overall.
For the foreseeable future I could see myself buying both EF and RF lenses depending on what purpose I had in mind.