So correct me if I'm wrong, you want to do outpatient FM (Primary Care) along with SM?
If so, that's the model that most common way to practice the hybrid mix. To be honest, full primary care sports med (only non-op orthopedics, etc.), jobs are harder to come by.
1. Funding your SM side is a key component as to why the above "Sole SM" sports for PC don't exist, the lack of patients to start up with. This is why alot (I would say 90%+) are FM/SM, as to build your SM practice, but funding not only your position, but your salary.
2. PCP's fearful of losing their MSK/SM patients? Heck no. TBH, most PCP's I know, along with the ones I trained, don't really want to do what SM trained docs do. Procedures are a biggie. If a PCP refers their patient to you, its done for a Ortho/SM reason (which you can deem operative/non-op), you aren't getting the referral from another PCP to manage their patient's DM. Thus their fear doesn't have a basis.
3. The cost of injections and xray isn't that much, honestly, majority of PCP offices I know have both. The U/S is a different factor, those start at a $100k+ (multi-probes, etc.), this might be hard to justify as a part time SM doc, as you need the patient volume to justify the cost (but again, this is where your ortho colleagues come in, they refer to you to do the injection therapies that are technically limited by palpation guided, or require imaging for proper guidance (but don't want fluoro, which is losing its grip), thus justifying the cost.
4. Thus, its possible. You'll have to work for it/design your practice etc.
Based on timing of things, you're atleast 8 years out from any of this, and by than, the market might be tougher (who knows?), as SM has picked up as of late.