Well it's down to the airlines in the end, the airport can only do so much, if airlines like Flybe don't want to operate from Cardiff or certain routes from Cardiff there isn't much they can do. One of their concerns will be winter as Flybe provide the bulk of flights and passengers during that period. It would be nice though if Flybe would get on and release the winter schedule so people know what will be continuing and don't look elsewhere.
Route wise hopefully they can persuade Ryanair to take over Dublin, add a flight to Faro and takeover Rome and Venice if not next year but the year after but i see that depends on how Barcelona does. Air France/HOP! would be a good replacement on Paris and the loss of Milan and Munich might as well encourage KLM to add more seats as well.
April saw an extra 21,525 passengers use the airport. Generally when airlines have added the extra seats and routes people have used them proving there is demand to fly from Cardiff with the right routes and airlines. Demand which does seem to be created as extra passengers for the airlines and not just taking them from neighbour airports.