I read in an answer to a question I read that a defense for if a question is accused of being non mainstream is applications of established science to new systems where they clearly apply.
One naive interpretation I can think of is that if it's possible to use the mathematics of a model in mainstream physics to answer a question then it's using an application of established science to a new system. If this is considered the correct interpretation then that would make it a viable defense when questions about things like faster than light tachyons or bodies with negative mass are accused of being non mainstream as on paper it's possible to insert tachyons and negative mass into equations that describe models in mainstream physics and get results. However I don't know of this argument being successfully used to keep open a question on something like tachyons or negative mass, that would otherwise have been closed.
Another naive interpretation I could see is that in order for it to be an application of existing science to a new system, for which it clearly applies, means that the system can only be interpreted using mainstream physics, however the problem I can see with using this criteria is that even well known systems that are predicted by mainstream models can be interpreted using non mainstream models. Also I would argue that if a new system can be interpreted using mainstream models or non mainstream ones then it is more natural to interpret it using mainstream models.
So my question is what determines applications of established science to new systems, to which they clearly apply?