The background is mathematics.
There are a few results I think are highly likely to be true, but proving them would take up some length, and they are not central to the paper I am writing. They also are not important enough to become an independent paper, so it is unlikely someone will come and prove them later.
So what should I do? Is it appropriate to say "the result A should be true, and one can prove it using method B"?
Edit: those statements are generalizations to a proposition and are not needed for the proof of the main result.