Perhaps, but I don’t think Canon is targeting the R3 for R5 owners. There are a lot more 5DIII/IV shooters out there, and a smaller number of 1D X (II/III) shooters, that are the more likely targets.
It’s a common refrain on this forum that, “Mark N of a camera isn’t much of an improvement over Mark N-1 in terms of [my favorite feature], so I’ll pass.” What people fail to grasp is that Canon is targeting owners of the Mark N-2 and earlier versions, as well as owners of ‘lower’ camera lines (xxD to xD, etc.). As I have often stated, Canon has data on who buys what and when, so for example they know how many 5DIV cameras were bought by 5DIII owners vs. those with a 5DII, 7D, 80D, etc. I suspect the latter group is much larger than the former.