I've started implementing this myself and I must apologise to the community for leaving this unfinished for so long.
The first working bits can be seen here: [https://github.com/nim-lang/Nim/blob/daae20e68c6b354cb09e842b742b7167245c91db/tests/concepts/tstackconcept.nim](https://github.com/nim-lang/Nim/blob/daae20e68c6b354cb09e842b742b7167245c91db/tests/concepts/tstackconcept.nim) You can try the new generic-concepts branch, where I plan to tackle the rest of the more complicated corner cases over the weekend.
