The real revenue generation of those non-surgical fields is still the procedures though--especially elective--the caths, and scopes. Oncology money is related to chemo/immunotherapy infusions (which still has a procedural CPT code compared to the treatments done by other 'medicine' treatments such as endocrinology for example)
From the point of view of the administrative goons, the perfect hospital would only do elective cardiothoracic surgery, elective spine, TKA/THA, elective cath (no STEMIs/ACS), scopes, and infuse chemo/immunotherapy. Everyone else can get bent.
Lo and Behold: At every hospital I've ever worked at, those "rainmakers" in the specialties that facilitate/provide the above dictate institutional policy and priorities.
I'm waaay out of my depth (I'm EM) but if you were financially motivated outpatient any IM is your background, your options would be to specialize in cards/GI to do procedural work (cath, scope) or something that uses a lot of infusions and you can find a way to own/operate or have a stake in the infusion center or home IV (some ID, rheum, onc).
The fact that most ID/rheum people I know are NOT killing it financially suggests to me that its easier said than done to get involved with that kind of thing though.