sucks for you, but not Enslaved.
They have done what, like 2 or 3 headlining tours already in the States.
This is an amazing opportunity for Enslaved, in opening for Opeth.
They will certainly be playing in front of many, esp younger, fans who have never seen them before.
It's good for Opeth too, as I would imagine some of their older fans who haven't seen them in a while might come back out this time around.