Can of worms time!
Given that the Valk and Vendetta now have the option to be treated as Flyers, is there any reason that Eldar grav tanks shouldn't get in on the act too?
My understanding of how grav tanks function suggests that they can achieve sufficient altitude to be considered fliers for the purposes of a 40k game played on a 6' by 4' board. The crew are also fully sealed from the external environment.
Maybe GW had this in mind and it's why our skimmers are currently so easy to hit in assault. But then why would they have missed the opportunity to reclassify our skimmers as Flyer (Hover) in the new rulebook?
Of course there's also the possibility that it would be game breaking...
I suspect that for various reasons the answer is 'no' but I thought it was worthy of discussion.