My main question is this:
Would it ever be considered worth it in one-on-one combat or 2v2 arena to spam Spellsteal on Druid HoTs if Lifebloom is up?
When a Lifebloom is put up, the final heal WILL be done regardless. The question is if you will let the ticks go on and have it happen after 7 seconds, or if you will grab those tiny ticks and have them heal him/herself for that final heal immediately.
If a druid puts up Lifebloom and Rejuvenation, Spellstealing looks like it wouldn't be that bad an idea from where I can see. I could end up stealing a fat, juicy Rejuvenation, or accidentally shatter that Lifebloom (does the mage get Lifebloom successfully still? Or is it "lost" on the Spellsteal because it procced for the druid?), or maybe accidentally end up with a Mark of the Wild or Thorns.
Unlike the other three heal-capable classes, a significant amount of the druid's healing can be stolen for a mage's use. But is it advisable? Or is it better to just burn up your mana bursting the druid down with damage?