It will be interesting as an operation. Having had a rough look at some numbers it will be a very targeted max TOW out of FLR and no doubt the same to limit the inbound load.
A guesstimation will be around a 12 ton payload so a semi-full A319. Expect fares to reflect.

Some rough numbers;
FLR rwy 05 (for landings) LDA or Landing Distance Available 1455m. Comparisons are GIB at 1528 on rwy 27 or JER rwy 26 at 1566m. An A319 at JER can bring in around 62-65 tons depending on met conditions but that is well in excess of it’s 61 ton max landing weight.
An A320 at GIB can plonk 63ish tons on the duty-free decks of the rock against a 66 ton structural limit. And A 320neo can bring 70 or so tons into JER which is well above its 67 (and a bit) tons limit.

Take off from FLR is going to be off 23 with a take off run available (TORA) of 1647m.
JER has a TORA of 1705m on the easterly end and a NEO could lift around 68 tons vs it’s max of 75 tons. A 319 could do 67 odd tons off the opposite end vs it’s max of 64 tons. And at GIB with a TORA of 1680m off the easterly end, a 320 ceo can haul around 70-73 and a bit tons which is around its max take of weight. Of course higher temps beyond the ‘flat rating’ temperature and any tail wind will start to dent those figures quite substantially. Of course those numbers are dependant on the obstacles and slopes of the runway and the net take off path of those respective fields and merely indicative of what might be achievable at FLR. I have no access to actual FLR data at this point.

So for a 319 with around a 42 ton dry operating weight and around 7 tons of fuel to fly back, around 12 tons would be the payload limit I would guess. It would make more sense to send the more efficient 32N in if a larger jet was needed but I can’t see much sense as again, tail winds in summer heat equal more seats needed out of PSA, BLQ or FCO.

Other operational issues already highlighted and as noted in other threads form last summer, the efficient 190 also had performance issues with FLR in windy conditions due to the adverse affects on performance with a tailwind.

So the Landing will be akin to a GIB one and the take off no doubt similar to a LCY/GIB blast off.
I hear PSA is still lovely that time of year and that the Jolly hotel is now an NH hotel by the stazione centrale. Chin chin.