Attempting to precisely define and codify what characterises a 'religion' is neither useful nor a well-defined goal. I think it would be entirely reasonable to,

Attempting to precisely define and codify what characterises a 'religion' is neither useful nor a well-defined goal. I think it would be entirely reasonable to, under the law, accept that if someone claims something is their religion then it is. It doesn't matter if they invented it, if they are the only one who believes it, nor if it is obviously satire; treat them all the same because anything else must necessarily be some convoluted and fundamentally broken criteria. Beyond that, the problem is that religions aren't just social constructs: they are granted special privileges under the laws of most countries. So the end result of this should be erosion and eventual dissolution of those privileges (though retaining the principle of freedom of religion and the designation of religion as a protected class against discrimination).