Bit more information to add to this thread, potentially save someone else the trouble of discovery…
2.8″ Nobby Nic on WTB i45 will fit and spin in a Stanton Sherpa but mud or out of true rims are definitely going to cause rub on the stays, not recommended.
Same tyre and rim combination will fit in an X fusion trace and has clearance around the tyre tread but the side walls run very close to the fork bulge; there’s maybe 2mm per side at 15psi, they almost rub at 30psi! Since low pressures are one of the alleged advantages of B+ I’m going to say this is a goer.
Now off to get a Trailblazer for the rear unless the Rocket Ron 2.8″ is in shops yet…