I really cannot see Stobart buying any other airports in the foreseeable future. One of the main reasons for selling part of the transport business was to greatly reduce borrowings, so they are hardly going to take on another debt burden in a hurry.
Yes of course there are constraints on the expansion of SEN as there are at nearly all airports, LTN included, but currently only 50% of the movement cap limit is used and there is no Southend Council limit on passenger numbers. It should be remembered that until the terminal extension was opened late last month SEN was capacity constrained at times with its current level of activity, so it wasn't in a position to go in search of another major user. I know for a fact that last year one such user approached SEN and they were told that their planned programme could not be comfortably accommodated so could they start with a 'toe in the water' operation. They declined to do that. The SEN response to something similar today would be entirely different of course.