It worries me that all these different (one might even say unrelated) features are proposed together, "just" to solve the problem of special traits. Adding static reflection and negative bounds and coinductive traits (and possibly more) is some really heavy machinery.
@hanna-kruppe I was not proposing to add negative bounds, just supposing that they would be eventually integrated in the language. To be honest I cannot find what is the last status on that topic. I know some fundamental issues were found that prevented an earlier integration in the language (just like specialization). Are they a dead proposal or are deeper explorations planned? Concerning coinductive traits my knowledge in this domain is too limited.
Of course, there would be many further uses for most of them, but if that is the motivation, then that should be the focus, not Copy and auto traits.
I initially considered Copy, auto-traits and derived traits were a sufficiently strong motivation. Now it appears people consider either good alternative features have already been added or that the status quo is sufficient. As you said a static reflection system may offer other interesting perspectives. Accessing the content of closures seems one of them.
Even then, I would like to evaluate each feature on its own merits (keeping synergies with other features in mind, but neatly separating them). If these features only make sense when considered together, they may not be as orthogonal as they appear.
The only feature I'm really trying to investigate is this kind of static reflection. I think my OP was published as an invitation to investigate and share opinions on the idea rather to impose some sort of conceptual model. Have anyone else expressed specific needs that may be filled by this very kind of reflection system?