I have to say No.
This should be possible!!! I have a friend who has a tonne of prime heroes he doesnt use... i have barely any. We both have about the same might but we play on different servers he's on ios and me on android. This would be a great idea to allow us to switch heroes with at least friends or guild mates and have it possible to friend people on different servers.
Make it cost a couple thousand gems. People won't be able to grind smurfs for great heroes nearly as easily, and there are plenty of people who would be perfectly willing to pay that. And there are plenty of people who would buy the gems needed to trade. A way to be certain of the hero you get would be great. That's what soul stones were supposed to be (at least that's what I understood). They were just implemented poorly.