You could definitely do that, I think the main thing stopping anyone is simply lack of demand for that specific feature. That, and also it might be hard to keep

You could definitely do that, I think the main thing stopping anyone is simply lack of demand for that specific feature. That, and also it might be hard to keep track of what things are properly reproducible; you can kind of only ever prove for sure that a package is not reproducible. It could be non-deterministic but only produce differences on different CPUs or an infinitesimally small percentage of times. Actually being able to assure determinism would be pretty amazing although I don't know how that could be achieved.