FWIW, here's our experience from last Thursday with 4 ships in port: RCCL Explorer OTS from 7 - 8, Celebrity Infinity from 7 to 10, Costa Pacifica from 8 - 7, Celestyal Olympia from 4 - 9; total passenger load over 11,000).
We got in line for the cable car in the morning about 10:15 am and it took 75 minutes. We got in line for the return about 4:45 pm and it took 70 minutes. The line to come back looked particularly discouraging in length, but because it is a narrower line, it moves much faster.
So it wasn't as bad as I'd heard (YMMV of course), though not nearly as nice as our trips in earlier years when we were the only ship in port. If Santorini wants to support this many ships, they really do need to upgrade their facilities.