We do have the technology to build HVDC cables from Iceland to Britain / Norway and we can expect the loss of this grid-to-grid interconnect to be < 5%. It's a different question entirely if it is feasible. It would be the longest sub-sea power cable ever, and the projected cost of $4 billion might be much too low.
In the current situation Europe would profit immensely by sending excess renewable energy to Iceland's pumped hydro and Aluminium smelters while using their geothermal baseload capacity. But in 15 years that might no longer be the case and by then the investment would not have paid off and there might be regret that the money wasn't spent on a different HVDC line like another North Africa - Europe link or Bulgaria - Caucasus (which has a lot of undeveloped hydro potential).
In the current situation Europe would profit immensely by sending excess renewable energy to Iceland's pumped hydro and Aluminium smelters while using their geothermal baseload capacity. But in 15 years that might no longer be the case and by then the investment would not have paid off and there might be regret that the money wasn't spent on a different HVDC line like another North Africa - Europe link or Bulgaria - Caucasus (which has a lot of undeveloped hydro potential).