Teleporting enemies via blackhole sounds like a good idea, but thinking about it longer than 10 seconds you'd laugh at how horrific that would be. Imagine two enemy allied armies bursting through some noob's defences. The noob instinctively thinks "TIEM 4 TEH BLAK HOEL!!!1!" and randomly teleports the enemies... into his ally's base.
Lol, now we all know that Blizzard wouldn't let any part of the game be *that* unbalanced but just the thought of poofing away those pesky battles you just don't want to deal with is hilarious. XD