The plan is to detect non-general solutions that assume some limit on input sizes. This will be done by adding larger inputs as I used to do before, except that they'll be hidden and failure on them will just make the solution rooted.
Since players can't select those extra inputs, I can use only a few and make them exceedingly large without slowing down rendering or testing. Note that loop unrolling, as long as it supports arbitary input sizes, will not make a solution rooted.
Regarding your suggestions: uniqueness information can't be overlaid on the existing charts as is, because the client and the server may have different thresholds. And as you implied, best-known rooted solutions don't affect scoring so they don't contribute thresholds. Technically everything can be presented (maybe in a new screen), but it's going to be tricky to explain the meaning of this information to players.