I have a feeling Gen 8 BH may be treated more like Let's Go BH than you might think. I don't think we ever adopted a meta where Eevee-Starter, Pikachu-Starter, or Melmetal--or their special moves such as Buzzy Buzz--can be selected alongside, say, Gen 5 mons. This means that a Blended Gen 8 BH may never be created, just like I don't think we can play Blended Gen 7 BH right now.