They are, however, open now. I was inside just hours ago and I am ready to submit my report.
Good news first: Wailing Caverns works (almost) perfectly. Only one quest is bugged but all the others are just fine. Naralex's old and decrepit disciple waddles along calmly, all the while warning us that "time is short" and we need to hurry. Gear drops are on point as well, and I had fun doing it (most important).
Now for the bad news.
You still should NOT queue for Scarlet Monastery or Scarlet Halls at level 35+. If you WALK (or fly) there you'll be fine; the dungeon itself is working with no noticeable problems. Teleporting there using the Dungeon Finder, however, will leave you floating in mid air, and if you try to move you WILL fall to your death. If this happens to you, don't move. TP out of the dungeon instead. It's a shame really; Scarlet Monastery was one of my favorites.
You should know that both Scarlet Monastery and Scarlet Halls work PERFECTLY at level 90 so no need to avoid them on heroic.
Gnomeregan also works, all the way up until the last boss. The door won't open, but a Warrior (and I suppose a Guardian druid) may charge inside. If he/she pulls the boss the door will open, but that won't matter since the boss will vanish. It's still worth doing the dungeon however, even if the quests inside don't work. The XP gained and gear dropped from mobs and bosses are just too good to pass up.