My hope is that either he's still alive and powerful (i.e. the Lurking Legend), or he's another successful clone after Stussy (no idea why Vega would do this though). I do still have this vague feeling that BB is also somehow tied to him spiritually and revealed eventually. The surgery sounds like a cool concept tbh.
My biggest hope atm is that if we go to Fullalead, Silver Axe, Ochoku, Shiki, and former WB/Roger pirates are there to really characterize who the Rocks pirates were.
Whats interesting is that for such a past threat (God Valley, BM and Kaido), its surprising that Oda keeps Rocks so relevent still (Blackbeard fighting Ochoku, Stussy, etc). Something really tells me BB is tied to it since Garp is also showing up at Fullalead, yet another witness to God Valley