I think there's some parochialism going on here. We do a lot of low threat environments and will continue to do so. If the threat steps up to a true ANTTP medium-threat environment, then rotary CAS in general is questionable without fixed-wing SEAD.
For the record T/R aircraft aren't going anywhere near that environment anyways if a true modern double digit SAM IADs exists, and if you're saying that you're capable of doing that - you're insane. Until a complete or partial rollback on an IADs is complete to an acceptable risk level, then we can let the slow movers into the game. Yes, I consider an Osprey a slow-mover. No MAGTF commander is going to let a company of Marines fly around in Ospreys with that type of threat.
I also have an issue with culture, if the Osprey community treats the OAS mission set like they do assault support, then there are going to be some major fuck ups before a change is established - something the attack communities have groomed themselves for decades. You may scoff at that idea, or call it parochial but dedicated platforms need that mentality. Going around looking for a fight with things that are actively trying to kill you requires a different mindset.
I also have doubts that a large Osprey can be as nimble as a Cobra or Harrier and provide the type of quick responsive fires that you would need for that mission set. Additionally, an APKWS or Griffin is not enough weapons yield for a true OAS platform. In reality to make that change you're going to need a 20mm or higher, mounts for JAGM/HF, 2.75/5in rockets, a targeting pod, integrated fire control systems/plumbing, and an assortment of GBUs. You can not slap all of that onto an Osprey and not make significant changes to the airframe. OAS needs dedicated platforms and I'm not sure what an APKWS or Griffin accomplishes that the KC-130 or Harrier already don't do aside from killing the occasional shitheads on motorcycles (which by the way we have plenty of UAS that can that do with significantly longer loiter time as well). The Osprey tanking idea is a good one and (speaking outside my realm) probably doesn't require as much currency/proficiency as CAS or DAS.
Ospreys should be focusing on what is going to kill them the most and that's from IP inbound, brown out situations, confined area landings, and high DA environments. I think the mishap rate for those situations warrants a better focus for assault support vice throwing in more missions that can (and are) filled by other platforms.