Which Dungeons are options for MM? Are they all equal chance of being used?

When I started playing I had "Rush" a few times. Not recently.
I've also had a new dungeon "Old School"? appear recently.

Only the official Cyanide dungeons are used in Matchmaking, with two exceptions. Roi Lorcan's "Dungeon old school 01" sems to have replaced "Rush" (which is no longer used) and "Cross" (or something like that) hasn't been used in a long time, if it ever was.

I'm guessing all of the dungeons in use have an equal chance of appearing, but it's difficult to tell for sure. There's no easy way to collect that data for anyone else than Cyanide.

The dungeons in the matchmaking are choosen randomly.

are going to be new dungeons added to ranked MM with the new enviroments (forest and dawrf cave)?