Excel don't have plans to base an aircraft there through next summer. Excel will base:
London Gatwick: 6x B737-800, 2x B767-200, 1x B757-200 and 1x B767-300
Manchester: 2x B737-800, 1x B767-200 and 3x B757-200
Newcastle: 1x B737-800
Birmigham: 1x B737-800
Glasgow: 1x B757-200
During the winter they will base:
London Gatwick: 3x B737-800, 1x B767-200 and 1x B767-300
Manchester: 1x B737-800
First Choice Air looks will base one aircraft at Cardiff over the busy summer period, but don't get your hopes up, i doubt it'll be anything more than an A320/A321.
Thomas Cook looks as if it will base an aircraft at Cardiff next summer, as i just tried it on their booking, but when i pressed continue it all just disappeared.
MyTravel will probably operate the normal and over the year will probably bring in a B767-300 to fly the SFB
route. Britannia, i don't know.