I like the use of the quotient set here. In fact, I would go on to use it more comprehensively: not only does our observer-moment define an equivalence class, but any particular context implementing it does, too. It could be a simulation, or a simulation in a simulation in a (...), a small corner of a more general mathematical system, anything. The point is that for any and every defined part, it too will always be part of a quotient; there will always be an indistinguishability of what's happening below.

As a result of this: does it mean anything to be 'a simulation'?

My own current thinking is that the Born rule - the everydayness of everyday life - is a reflection of how consciousness must function. I am just not entirely sure how yet...