They've done this before, when they covered their own song, Gravity, which they'd previously given to Embrace who released it in a completely different style.
It is interesting that Coldplay would perform The Astronaut alone, and it suggests they might release it as their own song... Why perform a song days after announcing a new album that isn't for said new album?
The Astronaut gives me a clear image in my head, particularly Coldplay's version. I imagine it being played at the end of a sad film when the tone changes and everyone will be alright as the credits start to roll.
The Astronaut being on Moon Music wouldn't be that bad, but not the greatest idea in my opinion. That would just make it seem, like they use it as a filler track, because they couldn't come up with enough songs. Also it would just be a little bit weird as well, giving a song to Jin, but then later taking it back. At least I wouldn't get it, but it wouldn't matter that much if it sounds ok in album context.
In recent performances hearing that Chris' voice is quite out of shape and it's so noticeable, despite of having a supporting backing track and a choir behind him. Honestly, I'm hoping they actually start using backing singers and maybe even some additional musicians on stage while touring. The hard truth is that Chris' voice just won't carry those high long notes anymore. It would suit well for Coldplay to have their stage more crowded and have some backing vocalists with them on tour.
Otherwise nice performances on SNL, Coldplay version of The Astronaut is nice, but Chris just doesn't do a good job singing it. It probably doesn't suit him, but otherwise it would suit well to their concert as we have seen already.
Also did Chris hit that guy's helmet at 2:05? It seems and sounds so much like that😆
Since wikipedia's story is shaped after the story that the labels want people to believe, or to be fair just the parts they want people to know, here's the real full story. Astronaut is a very-late-in-production track they were working on Mylo Xyloto sessions with the late Johann Johhannsson (I think it was a pre-existing arrangement or something of him), that went dormant until AHFOD(? I don't have proof for that but I think some people reading do) and then was handled to Kygo/Max Martin/Bill Rahko on MOTS and was eventually handled to Jin from BTS. I wouldn't be fully surprised if they'd release a version as a metaphorical answer to Jin and his situation, but atleast so far I'm not aware of such thing.