I dont neccesarly agree, I think the steamroom idea would boil your roots if not controlled, so you would have to measure the ammount of steam you're putting in/out.

You also need to think about your ventalation system ( if you're using one of course ). It would suck the steam right out of the room making it useless. I think that your plants would start showing signs of overwatering due to the ammount of steam you put in there and your water ph level.