I'm against this for reasons I described in the Redmine ticket. If we want to be backwards compatible, we shouldn't do it piecemeal, we need to do a complete audit of all Set methods and in every case where stdlib Set is calling a Set method, we need to change core Set to call the method instead of directly calling the underlying C function. That's likely to introduce race conditions that we'll have to deal with, and handling those safely will make the code even slower.

@jeremyevans I understand. It's kind of a bummer though because it's breaking our existing code. It would be nice if there was some escape hatch, but I'm not sure what that would be.

I think it's better to use composition rather than sub-classing if possible in scenarios like this. There are other code paths like IO where sub-classes of IO can override e.g. read and write in Ruby and it's a nightmare to maintain.