The way I read it, ACL have said that they have no intention of issuing any new slots at Gatwick so if someone wants to buy the Monarch slots they'll have to exchange slots they already own. The court judgment doesn't oblige ACL to issue those new slots, only the slots that Monarch have requested.
I find this an extraordinary judgment, I have come across the what is an 'air carrier' question before in relation to PSO routes and the accepted view has always been if the licence is suspended then you are not an 'air carrier'.