The spec discussion seems to suggest documenting the behavior diffs without either standardization or removal, right?  IMO that doesn't make the web platform better in any way.  Given the wide diffs in implementations, may be we should just try removing it?

Are there alternative APIs that can be used for the same things as these attributes? If there aren't, then I think the best next step would be to look a bit closer at the exact behavior of Chrome, Edge and Safari. Per https://github.com/w3c/uievents/issues/138#issuecomment-285261522 it's still an unknown whether content depends on the differences, so standardizing some intersection of behavior could still be possible.