I assume part of Stobart's support for the deal is that they have been guaranteed that WX will operate from SEN.
To be fair, both parties need this to work. WX need to prove that the SSJ can work in the western regional market and Stobart need to prove that SEN is a viable airport - despite its restrictions.
The initial opinion on SEN seemed to be very positive, now posters seem to take delight that it is taking time to find its place in the market. Remember that if it werent from Ryanair and, laterally, Go STN would be a much different place than it is today. New airports take time to develop and the SSJ seems like the perfect size aircraft to cater for SEN right now.