The problem with that is, what happens when your speculative code changed values in that region of memory that another core just wrote to. who wins? and how do

The problem with that is, what happens when your speculative code changed values in that region of memory that another core just wrote to. who wins? and how do you do it without now violating a bunch of other problems where one core sets up a memory fence and other things like that. It ends up incredibly complicated to decide what to do with the result that it's probably not worth the extra work.