I really don't see how he has a valid case against them as ADS-B data have been public for a long time. An expensive case with very slim chances of winning. Elon is literally scope creep personified. Several of his companies are at crucial stages of management yet this is what he chooses to spend time and energy on (or perhaps that's intentional?),.

Doesn’t need one. Even with SLAPP laws he can make life difficult enough for these sites, none of which are huge with substantial resources, to force many or most to give up and create a serious chilling effect.

He'd have to do this all over the world, good luck with that.