In the absence of an airport-run airline ("Esken Air" anyone) I do not see viable routes until the overall London market has recovered to pre-COVID19 levels and the whole cake has become big enough again to cut a small slice for Southend by steering away those passengers from the other London airports for which SEN offers an advantage (I would put my money on AMS and maybe DUB as the most likely candidates). All UK and foreign airlines that already serve LON will focus on rebuilding their market at their established gatewaysfor a long time and I doubt we will see any airlines without a London presence pre-COVID to enter this market in the foreseeable post-COVID future. Maybe a niche route.