I do wonder about single address space, I've seen a few experimental systems follow this strategy lately and it feels reliant on hardware less defective than we presently have in commodity user gui performance systems.
IBM i (OS/400) has had single address space, tagged pointers, and an number of other "novel" things in the loop for eons. Many people interact with it daily, indirectly, in most of your big box retail stores (think stores like Costco, Lowes, etc).
In what concerns ARM and SPARC platforms, memory tagging is happening and being adopted by Apple/Google platforms, in what concerns Intel, it was yet again another from their screwups.