From my conversations with Nosler (via e-mail) and the SAMMI specs.
The 28-Nosler is the same cartridge dimensions as a 26-Nosler except for diameter and neck length. The neck length change is only as a function of the larger bore.
The 284/26-Nosler "wildcat" is the same.
The parent case is the RUM/404 Jeffery's or if you like the parent case is the 26-Nosler and the parent of the 26-Nosler is the RUM/404 Jeffery's.
My work on this shows good accuracy but it seems my test barrel is "slow". Others are achieving faster speeds. I still have data to publish and some re-testing after using Tubb's Final Finish on my barrel.
The test mule is a Reminton 700 with a rechambered 7mm Win Mag "Sendero Special". I am waiting on a new Proof Research 7mm/284 barrel to build a new 28-Nosler on a Weatherby Mark V.