If I seriously wanted to move object destruction off-thread, I would use at least a dedicated thread with a channel, so I could make sure the dropper is done at some point (before the program terminates, at the latest). It also avoids starting and stopping threads constantly.

Something like this: https://play.rust-lang.org/?version=stable&mode=debug&editio...

You could have an even more advanced version spawning tasks into something like rayon's thread pool, I assume.