Yes, that is how C++/WinRT handles cascading deletion of COM instances, however when you are going down that route, it is basically a poor man's tracing GC.

However it just for the stuff you need it for. It's not all encompassing. It's not mandatory part of the language.

True, and unfortunately a reason why we keep having CVEs related to memory corruption.

There is a thread I came across on hacker news that does exactly that https://news.ycombinator.com/item?id=23362518 - this question reminded me of it

Yes, doing big drops in a subthread is a good way of avoiding pauses when dropping large objects of any kind.

Which is, of course, largely what concurrent GC is about.