[IshKebab]

I think all your points are answered by the background section of the RISC-V pointer masking extension spec:

> Doing this without hardware support introduces significant overheads since the pointer tag needs to be manually removed for every conventional memory operation. Pointer masking support reduces these overheads.

> It is worth mentioning that while HWASAN is the primary use-case for the current pointer masking extension, a number of other hardware/software features may be implemented leveraging Pointer Masking. Some of these use cases include sandboxing, object type checks and garbage collection bits in runtime systems.