Whatever a system is locked down is not a technology issue, it's about who have the key. You wouldn't be using MS-DOS today. Having more controls over what the applications are up to would be beneficial for the user. The modern multitasking systems have their origin in the time-sharing systems (which are exactly the locked-down ones) where security was "protect the admin's authority, protect users from each other" and hence "what application does is by definition authorized by the user that started the application". Then we started adding some "protect user data from the programs" safeguards but on desktop it always was an afterthought and on mobile the new security model is "protect the platform vendor authority from the user". Sadly a new API designed around "protect programs from each other, enforce users authority" never materialized.

But all of this is about IO. What OP is talking about is memory model and the changes they propose is not about "don't let the unauthorized ones do things" but rather "make it harder for a confused deputy do things". This one is pretty uncontroversial in its intent, though I personally don't really agree with the approach.