Seventh Flight Freedom waiver?

Icelandair can fly across the Atlantic without stopping in Iceland if they want to. They do not need to reach any additional agreements to be able to do it.

would IcelandAir be able to reach agreements to receive the 7th flight freedom so they could skip Iceland?

This really would not be feasible. icelandair operates on a hub and spoke model with Keflavik being the hub. People fly from various points to Iceland and then switch to flights to various other cities. I’d speculate that the majority of the people on your flight won’t be heading to Glasgow. It isn’t as though they could just move their hub to some other location at the spur of the moment.

Iceland is a party to the EU-US Open Skies Agreement (yes, it's not in the EU but it along with Norway acceded to this agreement in 2011). So Icelandair, being covered by this agreement, is permitted to fly from anywhere in the EU to anywhere in the US.

Whether it's practical for them to operate without their Keflavik hub is another question. It has actually been done on a temporary basis and also in fact during a previous volcano eruption -- in 2010 during the Eyjafjallajökull volcano eruption, Icelandair shifted a large part of their operations to Glasgow in fact. But I think things would basically have to be as equally serious now as it was then for them to do this.

A few years ago, conditions meant Iceland Air couldn’t fly out of Iceland for a bit. They proactively rescheduled my brother and his wife on another airline to assure they had a flight.

Let’s hope for the best. I had a 2010 flight cancelled (as did millions of other people) because of an Iceland eruption and it was 2 weeks before I could reschedule flying a more southerly route to our destination.