I have looked at the website and am not sure how it works. Is it just one ship and why don't they stop somewhere with more and cheaper airfare?
There is a section on the website on ''newbuilding'' with designs for new ships under construction.
Maybe they could add some EasyJet flights from Miami to Barbados at typical EasyJet prices - which make Southwest look expensive.
Where I think this could be quite interesting is island hopping before or after a timeshare vacation. One could use an open jaw ticket combined with a couple of nights on Easy Cruise to see a couple of other islands. Say, fly into Grenada preceding a Barbados t/s exchange on Thursday, take Easy Cruise to St. Lucia and then to Barbados for the exchange, and fly home from Barbados.
Alternatively, one could do St. Vincent and Martinique after a t/s exchange on Barbados.
I don't know that I would want to do a no frills cruise for 7 days, but island hopping for a couple of days could be quite attractive.