Actually, scratch that. Its feasible to do. The implementation that supports unicode escapes depends on using a regular expression, so is costlier. I have a version I can push that actually tracks on the source file whether it contains identifiers with unicode escapes, and if it doesn't then it can use the existing `indexOf` logic, which should be faster:
![image]([URL]
I might wait on that until after this PR, however, as I'd need to also add fourslash tests for find-all-references which could be time consuming and could possibly wait until after 4.1-beta.