FI has been marketing MSP-KEF-(Insert Popular european destination) for a long time. They are set up very similar to the way DL does connections in NRT with a list of top US and European stations. They have a long history of being consistently cheaper than any of the majors.

I'm a bit dubious how much of a bite a MSP-KEF is going to take when it seems like most travelers end up continuing onto Europe. I believe FI still offers a free stopovers in KEF. Moreover, I can't remember DL trying particularly hard to match FI on fares, so it's a bit weird.