A side effect of asking an uncommon question is that part of the collective user base will err on the side of caution and come up with potential issues.

Putting this a different way, is swapping one chain between two bikes much different than swapping multiple cassettes/wheels into one bike? That’s something many people here do, and without dedicating a different chain to each wheel.

Edit, and this is just a curiosity, I wonder if a chain used only indoors on a trainer would have a longer life due to not experiencing as much road grit? If most wear particles come from gradual chain breakdown it wouldn’t matter, and if they come from outside sources it might. How does this compare to outdoor bikes with well enclosed chain guards, if such a thing still exists in any real numbers? I wouldn’t let that stop me from swapping the chains, but that’s just me.