Ski, we don't understand all the details but the basic issue at hand here- that the sun and the other stars are powered by fusion is very clear.
Given all that we don't understand about the sun, I submit that it's entirely possible that the sun is powered by fusion even if it is 32 miles wide. We just don't understand how yet. I'm honestly perplexed why this is never an issue in RE but it is always one in FE.
Just because we don't understand everything about the sun or nuclear fusion, that doesn't mean that we don't understand enough to realize that a 32 mile diameter sun could not possibly be powered by nuclear fusion.
I see no problem with this. All we have to do is postulate an unobserved mechanism, much like physicists do with dark energy, dark matter, dark flow, gravitons, parallel universes, hyperspatial dimensions, etc!
It needs a placeholder name, of course. How about fusionite?
There's an important distinction there. In those cases, they aren't just using placeholders. They are taking theories that have been already tested, and trying to deal with apparent discrepancies. Then, they make predictions based on those terms. Thus for example the standard hypotheses for dark matter all make different, specific predictions, and scientists are busy testing them. Thus for example, neutrino mass was a popular explanation for dark matter at one point, but careful experiments showed that it cannot account for more than about 5% of dark matter. Similarly, some of the more exotic possible particles have been ruled out. Thus, much of the dark matter comes down to likely being low-albedo conventional objects (such as brown dwarfs) or particles arising from supersymmetry or similar constructions. One is welcome to make place holders but one can't stop there. One needs to then ask "ok. What can I put in this place holder that fits what else I know? How can I go about testing it?"
The philosopher Imre Lakatos talked about this a lot. To summarize his view of things, it is important to distinguish between fruitful and non-fruitful theories (he actually talked about "research programs" but for our purposes this is the same thing). Both get "defensive hypotheses" attached to them, essentially hypotheses which would protect the theory from falsification (as dark matter protects our theories of gravity). But a fruitful theory generates not just defensive hypotheses but makes useful predictions, and generates other hypotheses about related issues which can be used to make interesting predictions. If a theory just generates defensive hypotheses with no content then it isn't fruitful, and should be rejected. The standard theories of gravity, and stellar fusion have both been fruitful. The theory that the sun is 32 miles wide hasn't been very fruitful.