I mean, roughly, that not only are the two empircally indistinguishable,

Don't you mean "have been indistinguishable up to time T"

but that I don't even see a reason to care about whether I'm "in a simulation" or not, and it's not even clear what would qualify as a simulation..

Simulations support counterfactuals, such as shutdowns. getting out into the real world, etc.

If we're given assurances that things you might care about, such as being abruptly halted, aren't going to happen, then you might have nothing further to care about....but it is difficult to see what such assurances would consist of,