I think it's unrealistic in the longer term to think Ryanair is only going to operate one flight a week to Tenerife, so there's bound to be more routes to follow. Maybe not at first during the winter season but by Summer 2015 I would expect some additions.
Obvious routes to me would be the usual bucket and spade routes such as places like Alicante, Faro, Lanzarote, Malaga, Palma etc. especially if they operate without a base in Cardiff, but then there's an overlap with Vueling on some of those.