You can currently use the !despecialise command to remove wizard school spec IF you have barred a school that you have ESF in. You can currently take PSK for a school without taking LSF & PSF if you have ESF & are specialised in that school. PSK gives all the benefits (Spell DC & improving spell effects) that PSF does
By using a combination of the above, you can specialise in a school, take the PSK feat, despecialise, and repeat for all schools.
If this is a bug, here is a bug report
If not a bug, please advise and i will abuse the hell out of it optimise my build around it
Before you start hunting this down, note that it is just something we've theoretized about on Discord yesterday and have not actually tried doing it. I don't have a high level wiz I could reincarnate to try this but if someone else does, it might save some dev time in case it doesn't actually work.
I have only tested the individual components (the ability to de-specialise and skipping LSF & PSF by taking PSK). I was told using these in conjunction might be considered an exploit and was seeking clarification.