I think Luton definitely showed it can support a Copenhagen route in pax numbers but maybe the yield wasn't there.
I think at one point it was the most popular route by pax numbers from the airport, when easyJet and Ryanair were both operating it several times a day.
Ryanair forced easy off the route and then pulled the route themselves. I guess it remains to be seen how they would react if someone else tried it again.