If I had a day or two to spare, I'd be up for a stopover in Iceland, and given that Icelandair make a fair go at plugging a transatlantic stopover in their marketing, I suspect quite a lot of other leisure passengers who are not too time poor are up for it as well.
The vast extent of FI's US & Canada route network (relative to population) suggests they handle a fair volume of transfer pax through KEF. Adding DEN next?
However, serving this market should mean there is spare capacity on ptp too, although my experience has shown that when an airline operates from a spoke to its hub, it can often still be cheaper to take a connecting service with someone else between these two points. Hence, there should be room for a loco on this route, but 3?