I can certainly understand wanting to only include the universal sorts of things and that’s completely a valid option for any of the various discussions about what should/should not be included - the reason I’m asking here is because, at some point, there should be something that comes from the CommonMark Team/Community/Whoever that says - “we’ve reviewed this idea and discussed it and we don’t think it’s universal enough to include in our spec.”
And then there can be a sort of … end to the discussion.
If people have spent six years throwing around ideas for spoilers, eventually we should probably just say, “Yeah, we don’t think spoilers are universal enough to make a standard.” (For example) And then, of course, we can start discussions about why they should be. 
If there’s no indication that something’s not happening and people like @codinghorror are saying things like -
… it feels like it’s actually going somewhere (for both tables and spoilers), so you’re just … waiting for something to happen. I understand completely if this is not a priority - I’m walking in off the street and don’t actually know what the priorities are right now or if anything’s actually moving forward with CM… but I’d love to at least resolve some of these requests.