I'm definitely not a doctor or a pain management specialist, but I'm definitely puzzled by this suggestion. Buprenorphine (Suboxone; Subutex) definitely has a legitimate place in the field of pain management, but only in certain situations. For instance, Buprenorphine is going to be most effective for folks with no history of Opioid dependence/tolerance. Most people I've ever known with past history of Opioid tolerance no longer see Buprenorphine as a viable option for pain control.
Buprenorphine has some pretty funky pharmacology/pharmacokinetics that make it even more difficult to use effectively for pain management. It's a partial agonist/antagonist and its pharmacokinetics are not linear in scale; basically, the effects of Buprenorphine become radically different as the dosage is increased. Already, you can see how Buprenorphine adds a level of complexity to an already complex situation that I don't feel is necessary when the option is available to simply use more of a standard Opioid agonist.
I don't have a ton of experience personally or research-wise regarding these sub-maintenance dosages of Buprenorphine. The vast majority of my knowledge concerns the usage of Buprenorphine in higher dosages of at least 2mg Buprenorphine at a time. The aforementioned weird pharmacology of Buprenorphine really starts around the 1mg-2mg mark. I'm not going to overload you with information here, just know that Buprenorphine becomes less effective as an analgesic the higher the dosage goes.
Given that the dosages of Belbuca are fairly low, I'm not gonna say it couldn't work. There are some grey areas regarding Opioid usage that we're still trying to understand with more clarity. For instance, there is good information out there seeming to imply that Ultra-Low Dose Naltrexone (ULDN) therapy is some kind of holy grail in maintaining the efficacy of Opioids over time. Naltrexone is of course an Opioid antagonist, so you get why I use the term "mystery" here.
With that in mind, who is to say that using an agonist/antagonist like Buprenorphine in low dosages in conjunction with a full agonist couldn't check some kind of mystery box?
I think it's something that is at least worth trying. Your doctor will give you some brownie points for playing ball with him and who knows, maybe it will actually be what you're looking for. I would just be mindful of your feelings after starting the medication. Monitor for signs of withdrawal and obviously increased pain. You can always stop taking the medication, so I don't see the harm in trying it.
Please, whatever happens, please come back to us with your story. We have a serious dearth of information regarding this kind of Buprenorphine usage, especially with other full agonists. Your experience could be incredibly insightful and helpful to others, not to mention I'm just curious as an avowed drug nerd.