The seat maps suggest numbers are a bit better in July and early August, but nobody is going to sustain a route that works for 6 weeks of the year.
A couple of things in Cork's favour are that the airline is adding aircraft and they may be willing to tough it out to establish the route and that the sector is short enough that it can be used to regain time on a delayed aircraft (as they are used for flights to the US in the overnight slots, there's no getting things back in order overnight). Against that, they have cancelled a number of non-working destinations and there are a few UK airports (Cardiff, Newcastle, Liverpool) with no Iceland service and which could offer a similar sector time.