Laser blinding weapons are available from some countries, and probably the UK has its old Outfit DEC installations (allegedy brought down some Argentine aircraft in 1982) in a warehouse somewhere. However, once it was realised that such weapons tend to even up the odds for all users, and threaten to render piloted aircraft highly vulnerable (hence the BAe P.125 project with a 'buried' pilot), then the major western powers were happy to go along with 'banning' them, if only to slow their spread.
If (and that is a big one) a laser could be put in an F-35, it seems silly to do so.
1. Their range is limited, so the F-35 may need to get within visual range of a target (6nm), negating stealth - even if stealthy turrets can be made
2. There is a need to counter structural deflections and airflow etc. for aiming, meaning that speed and manouevre are likely to be limited
So these two mean you would have a supersonic, stealthy, manoueverable aircraft flying slow, steady and in visual range. Why? Plus it is not free - a probable need for major flight control software updates etc. to allow turret(s) where the lift fan will not be cheap, and structural mods would be needed, plus propulsion system mods too - the lift shaft is not used for flight above c.250kts.
Probably much easier/cheaper to use a new platform (UCAV?), or even a C-130. And then once China puts one in an AN-12, or on a merchant ship, and then someone figures out what that could do to a USMC landing in support of Taiwan.... more 'banning' will be called for, IMHO. Better not to let the 'other guy' have it than to have it yourself.
Regarding PCB, modern engines (even 1980s tech level) should allow 'minimum' PCB temps (800K) more for balance than for total thrust in VL. As Boeing found out, making the jet balance on dry thrust moves the engine too far forward (or adds ducting/volume as in old MDC 'Cactus'). What this means is that all the things of buckling decks, swabs over the side etc. are more to do with the core flow than PCB, i.e. same as for any naval aircraft. Hot Gas is highly configuration dependent, but alleviation is possible using rolling or creeping VL, nozzle 'blipping', front nozzle area variation to raise the fan surge margin etc. And stealth was an issue for the P.1230 that the UK studied with the US (Harrier configuration) as the hot gas flowed along the fuselage which meant IR emissions over a wide spectrum (plume and body radiation). On other configurations (P.1216) it was much less of an issue (plume only).
As LowObservable basically says, there is little point using a supersonic jet for a subsonic job, unless you want STOVL and there is only one aircraft type available with that ability. Hence the F-35B. But a Harrier 3, if funded, would probably find a market in USMC/RN, not that they would be able to get it funded.