Two directions instead of two features, if I may.
Social part:
- An option to mark another solution as inspiration or previous
version (which you improved, or so you think). With pretty graphs, or
just github-style relations display.
- Comments for solutions and/or voting system.
Solution management:
- An option to delete or replace your solution. For small incremental
improvements, for example.
- Somehow separate "I've solved this!" and "Everybody look at my neat
solution!" kinds of uploads. Uploading your solution feels validating,
but not every solution is worth looking at. Some sort of explicit
"publish" button, maybe?
More katas is a must, too.