It's actually pleasing to see it's "passenger experience" that seems to be the problem at Stansted. Personally I've found it to be ok, with very good staff control of early morning check-in (moving passengers forward on flights that are close to closing etc.) and very sympathetic security staff who was very calm and helped out as much as possible when there was an issue with the clear bags we had toiletries in. If Stansted's problem was more to do with the size, layout, amount of facillities or something else infrastuctual, this would be more difficult and costly to solve and change of ownership would ultimately make little difference, especially in the short-term.
Hopefully, new ownership will improve passenger experience and do expect that to be the case. MAG for instance, who probably has the greatest chance of buying Stansted, is a great airport owner who run very successful and smoothly run airports. I trust an airport owner like MAG to push ahead for better rail connections also.