It's nowhere near that uncertain. "Memory safety" is hardly a subtle property and it's been well-understood since we figured out how to enforce it in garbage collected languages.

The only uncertain part is which rules unsafe code has to follow to maintain it- it currently comes down to "whatever LLVM optimizations won't break," which is in practice what C and C++ programmers deal with already. Things like your link are work to improve the situation beyond C and C++.