You certainly won't see Ryanair at SEN (other than for maintenance as is the case now anyway) as the runway is way too short for commercial operation of the 737-800.
There is an airline (other than Flybe) who have very tentative plans for a route network out of SEN, perhaps in 2008. Before you ask, I cannot say who it is as I received the information last month on a confidential basis. If I hear anything than I can mention it will appear on the Southend thread.