Fast cruiser
I take your point about the cost as bmi is very overpriced out of EMA. However, I think you will find a 737 with 148 odd seats in it far more cramped than an EMB145 with 49. At the end of the day it depends on individual passenger preferences.
I see Go as having two opportunities at EMA. They can either go head to head on the routes that bmi are already established on or they can compliment those routes by offering destinations such as Barcelona, Milan etc. that bmi don't serve.
Good news for EMA as an airport though.
ES