Right now all we have are dummies for dps to practice their parsing. It would be awesome if we were able to get dummies for tanks and healers.
Maybe we could just have a dummy that, every few seconds, does an attack? That way a tank can practice applying their debuffs and buffs while still learning watch the boss and time blocks. And one of those attacks could be a one-shot (or high damage) channel attack that needs to be interrupted. That would be a way to teach some tank fundamentals.
Or for healers, the dummy could apply some kind of purgeable / out-healable DoT, or you could have the heal a few moving targets to simulate what a dungeon run is like.
This may be too complicated for a simple dummy, but it'd be great it we could get more support for teaching the fundamentals of tanking and healing.