Dig has been in the voting several times now, but never gets picked. I imagine its time will come eventually.
Twin has a number of problems that have kept it from being considered so far. The first has been that it’s just too close to the banning for us to really learn anything. It’s getting far enough away from that ban and Modern is sufficiently different enough that I could see doing Twin eventually. The main problem is that there really isn’t a good deck to use as the test deck’s control. Twin’s construction and gameplan have never really been replicated, so I don’t know how to approach building the deck or how to compare it.
Ponder is tricky because I’ve already tested Preordain. That card didn’t impress, but it’s results were also suggestive that I wasn’t taking full advantage either. Ponder is in a different league to almost every other cantrip, and I imagine the test would just confirm that. It’s not a definate no, but don’t look for it either.