Programs also access memory outside of the above list, like pointers in the cookie jar, the buffer returned by the Iorec XBIOS function, etc. ... so maybe it's possible to implement such a feature, but it's certainly a lot of work to get that really right.
Good point. However that's exactly the thing -- we don't have to get it really right. It could be just a warning in the console. So if I, as a developer, see that 0x000005a0 is being accessed "illegally", I can safely ignore that warning and continue my work.
This is meant to be purely a developer's tool, nothing for regular users (it would be disabled by default).
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