Of course, MSFT/Apple etc will abuse it to kill apps they/govt don't like.
Code signing is a bit like gun control. It really doesn't solve the problem at all. It just pushes it up a level, and makes things more difficult for legitimate users.
It also lines up incentives such that the preferred model of software distribution shifts in the grand scheme of things toward for profit code.
While code signing is a neat technical solution, it's still a technical solution parading about as a solution to a social problem. And the social problem it is a solution to (that of untrustworthy folks existing) is not in any way mitigated by the act of signing as mentioned previously.
Although it costs $19 or $99 to sign up, one time.
They could enable this for win32 apps but they want to push things towards the walled garden.