Excel already do a weekly charter to St Kitts (bags and passengers not always well matched up, allegedly).
This part of the Caribbean is still pretty difficult to get to, but then again it is a fairly small market (both St Kitts and Nevis only really have one super hotel each, both heavily targetted at the US market). The 4 Seasons on Nevis even takes people from SKN to Nevis by boat, as NEV runway can't take anything long haul (despite swanky new terminal).
Lots of construction going on at Tortola, but I don't think that would be enough for long haul.