Theoretical knowledge, language proficiency, medical requirements, flight training and testing should be proportionate for a rating which would require a 600ft cloudbase and 1800m visibility for take-off, landing and at an alternate with approach minima no lower than 'full IR minima' +200ft for precision and +250ft for non-precision approaches.
The problem with such an approach (no pun intended) is that yet again it will not work with the existing ATC framework - which simply operates on the basis that the pilot has the privileges for the
published approach.
There will never be any mechanism in place for anything different, not least because nobody will ever be able to prove at which point the pilot became visual.
This is why the IMCR legal privilege is the
published approach. The extra 500ft or whatever is just a recommendation which in a single crew / private flight scenario is totally unenforceable.