Not completely in secret, obviously, as they're showing people but exactly which former Psygnosis and Sony devs are involved isn't being disclosed as "some are still working for others".
The new game's called Formula Fusion but making things sound a touch dodgy is mention from the studio involved that "we have never said anything about it being from the 'original' crew: Nick etc" (meaning Nick Burcombe, the original lead designer of the series). A Facebook post acknowledges that the team are "being 'ultra' careful over the claims we make so we can't be accused of false truths". So for all we know it could turn out to be the cleaner and that guy in accounts. But for now let's assume it's real developer people with a history of making racing games with jet cars in them.
Look, a trailer with jet cars:
According to developer R8Games Facebook page the studio can't talk about who's involved "until it becomes more official" because "some are still working for others atm". From the talk of sorting investment and mention of "very early days with partners" it sound like no one's willing to risk too much just yet. Especially as according to the studio "publishers won't touch another Wipeout at the moment".
As a result the mystery team are funding it themselves and looking for investment. Hopefully, if they're successful, they'll whip off some masks Scooby-Doo style so we can all shout you "IT WAS YOU ALL ALONG".
If you want to see just how Wipeout it all gets take a look at some of the concept branding: