There have been considerable increases in traffic from Ryanair (+2 aircraft), WizzAir UK (9, or is it 11 new aircraft based) and easyJet (significant increase in based fleet). Blue Air have also increased their presence. That goes to show that Luton is a desirable base, and money can be made in the low cost sector with based aircraft.
However, it squeezes the capacity available for new entrants. More based aircraft are really out of the question, so foreign- or away-based carriers operating limited services off-peak will be the target for new growth.
Whilst Heathrow is at capacity, Luton has gained some overflow from there (Tarom and El Al). More could follow. However, Gatwick seems to be able to accommodate growth, and has gained numerous operators in recent years. Stansted too has attracted some new carriers, but tends to attract those who are financially weak (Primera, Cobalt, Wow to name but three). North-of-London ops will be contested with Stansted, which has greater capacity, better terminal facilities, but a smaller catchment population, and worse surface connections.
Hopefully, T2 proposals will emerge soon, and ways will be found to increase runway capacity.
Anyone looking for lots of new carriers is likely to be disappointed over the next few years.