If this ever came into fruition, that would be awesome.
Interestingly enough, have seen a post PM&R + sports/spine trained go from almost a purely outpatient sports medicine MSK group practice to inpatient rehab (unsure why though). Was making well over 300K+ at the MSK clinic working 40 hour weeks. I guess being a procedural/needle jockey wasn't stimulating enough for the attending I know. Or the attending left for better money at inpatient work (as I recall, very $$$ minded individual). So having other training in either IM/FM/PM&R gives them a chance to leave to other aspects of their scope of training.
For some I know, sports medicine can get boring quickly if not surgical. Knew someone who considered PM&R for sports but found their sports medicine elective in medical school so boring and they ended up applying to a surgical specialty unrelated to MSK (not ortho). Some, it's amazing -- for example, know an EM/Sports medicine trained doc who loves working in outpatient MSK for a much lower pay/hour than working in an ED (chill hours and a colleague who knew the EM/sports med doc well said EM residency burned them out pretty badly).