Leeds-Bradford - My first reaction was that this never worked from Cork or Shannon with their larger catchment, but am I right in thinking there is a history of substantial emigration from the North-West to Yorkshire? Possibly strong family ties may produce a boost.
Heathrow - Almost every Irish airport, including Kerry, or even an effectively closed airport like Waterford, could support a connection to Heathrow. The problem is at the other end. If/when a new runway is built, there is likely to be serious competition for access.
Southend - Might work, but I would have thought increased frequency on one of the other London routes would be a better bet for a capacity increase.
Sun Routes - There does seem to be a bit of scope for growth here, both in terms of capacity on existing routes and some potential new ones. Fuerteventura, Dubrovnik, Verona, Nice and Lisbon could be possibilities for new routes, although too many launching could cannibalise each other. An important figure here is when people from Galway have a choice between Knock, Shannon and Dublin for existing routes, how many opt for Knock.
Inbound tourism - The place to look for inspiration here is Kerry Airport, which has pitched their tourist offering to Germans to such an extent that they overfly Dublin, Cork and Shannon into Kerry. Kerry can't even support UK routes outside London, but makes these routes to Germany work. The route to Cologne/Bonn is a start in that regard, but there's a lot more potential than that.
One other one to add to the mix is Polish routes. Cork and Shannon both support in the region of 75K-80K passengers per year to Poland and that before the route from Cork to Katowice launches. You'd have to think that Knock could support some kind of frequency to Poland.