True, you cannot become subspecialty pain boarded without an accredited "pain" fellowship. However, you are misunderstanding a few points.
1. The "other pain board (ABPM)" has only ever been reconized in 3 states (CA, TX, FL), maybe 2 now.
2. In most instances, you don't need to be "pain" boarded for procedural insurance reimbursement. Take a look at spine injecting radiologists as an example. You may need hospital priviledges for priviledges elsewhere, but that is more of an issue of economic credentialling (e.g. exclusive hospital contracts by OR anesthesia groups), not necessarily your pain board status. And finally, if you go to work for a large group (Ortho/Neurosurg), or if you do procedures in your office it won't matter.
and if it does become a problem, there are already multiple solutions being developed by several key organizations, one of which is your own specialty board.
Read here:
http://forums.studentdoctor.net/showpost.php?p=6196461&postcount=46
http://forums.studentdoctor.net/showthread.php?t=501642&highlight=ABIPP
3. You've probably heard that reimbursements for interventional pain procedures are dropping. Once that is all said and done, I doubt anyone will be willing to put forth the effort to enact legislation as to who and who can't perform procedures.
In 5-10 years, for a graduating PM&R resident wanting to do sports and lots of procedures, I would go for CAQ sports med and CAQ Interventional Spine (or equivalent), 18 month fellowship. Get the training you need in as little time possible so you can get on with your life. Efficiency is key.