Not an awful lot, it has to be said; traffic is down this year, and last year was already down on the previous year.
However, the imminent department of BE from the LGW route is likely to stir things up a bit; latest from Rumour Central is that - wait for it - GR is interested in taking up the lease on three (soon to be) ex-BE 195s, expected to come off lease this year. These would operate primarily ex-GCI to LGW, but possibly from JER too? A lot has to do with the fact that LGW is trying to price props out of LGW and has already succeeded in doing so with BE.
There's a lot of obstacles in the way, particularly E-195 performance ex-GCI, but if Trip and Azul can operate them from Rio's SDU, then it should be possible; perhapss some modifications may need to be made.
Of course, the big question is whether U2 would want to fly from JER to LGW and if they do, would they want to base an acft here overnight. Some rumours say yes, others - no. However, it would clearly be very important for the JER market. A BE operation would be most welcome, though presumably they would only operate two or three times a day, so it might still be a drop in capacity.