I don't think it would have any effect, except to annoy high-level PCs who want to focus on their strengths.
Except Elves. Once they learned they could effectively get +7 Con, they might be happier.
Oh, and Dwarf Sorcerers would become common, assuming the PCs started around 18th level.
Er, are you trying to address a problem or issue with this rule?
Basically, I don't see any advantage to doing this; it just adds one more thing for the pcs to keep track of. But maybe I'm missing the underlying issue?