It will always be difficult to attract new business knowing that FR will jump on any competition in a flash, sometimes less is more.
I'm not even sure if that is even an issue. Ryanair likes the secondary airports generally speaking, so any airline that will offer a primary airport is not likely to get any direct competition from Ryanair. Remember also that Gatwick has more EasyJet now than Stansted does Ryanair and yet that doesn't seem to be an issue with loads of direct competition here, there and everywhere.
Furthermore, EasyJet have recently abandoned some of the most popular sun destinations in the last year or so because they are now going from Southend which leaves Stansted with Ryanair as the only option on a lot of those routes like Alicante, Barcelona and Faro. I don't the competition from Ryanair was to blame for this, they have had Ryanair alongside them on those routes for several years. Instead, it's just their interest in Southend, in which Stansted now pays the price.
If a new owner really wanted to get things going, they should try and get Jet2 in. I know Jet2 seem very reluctant to go to London airports but they do use Stansted for cargo flights and do compete strongly with Ryanair already and have tried taking on some of their routes elsewhere and have been successful. Also with EasyJet ditching those key routes creating a large slump in the capacity, what better time is there for Jet2 to try and get in and fill that space.