I'm actually moving this to a public category for further customer comment. I agree this is a small change, but would be really helpful. This typically comes up when someone else created the report, and I'm trying to figure out what field they used but can't because it's been re-named.
Would love to see this enhancement! When going back to reports where a field has been renamed, I have resorted to finding the field I think is used and attempting to add it in order to confirm if my assumption was correct.