This technique is mostly a garbage collector, as I see it. Postponing memory destruction until the stack is empty is a special case of deferred reference counting [1], where sweep can only happen with an empty stack. If the "soft pointers" are implemented with reference counting, that's also a type of GC.

On the other hand, the tagged pointer implementation strategy for "soft pointers" isn't really garbage collection, but it does have much of the same overhead. Pointer reads must check the tag ID and throw, which is like a read barrier [2]. Writes through a pointer must do the same, similar to a write barrier [3]. And that's not getting into the overhead of multithreading; I see no reasonable way to implement this scheme in a multithreaded world. I expect that a fast GC without read barriers will significantly outperform this scheme. As much as everyone complains about the speed of GC, garbage collection is hard to beat!

[1]: http://www.memorymanagement.org/glossary/d.html#term-deferre...

[2]: http://www.memorymanagement.org/glossary/r.html#term-read-ba...

[3]: http://www.memorymanagement.org/glossary/w.html#term-write-b...