Bottom line is, Sony is still calling the shots.
For all we know there could be other tracks for 2048 already partially built in among the SL archives, if any new Wipeout content were to emerge, I imagine it would be for the 2048 craft handling.

I doubt SL were working on any other HD/FURY tracks [conversions from Pure / Pulse] as HD whole reason for being was to be the first download only game at the PStore, and as such would of had a file size limit/target imposed on it before work was begun.

If anything new were to appear, I think Sony would be wanting to do something radical with a new Wipeout, as it has tended to do so with previous releases over the years.
I wouldn't be surprised if the next new Wipeout [Inevitable now that Sony has proven that it hasn't forgotten the franchise] would be VR compatible, just to help bolster VR headset sales, which I think have stalled [I certainly don't see people on my friends list that I know have VR headsets ever using them since they first bought them], I don't know about the UK or USA, but here in Australia, I'm no longer seeing VR demonstrations being made available for people to try, it's as if the whole VR thing has already run it's course and has been relegated to history.