Yeah thats a common fantheory I also Like very much.
I think it will be revealed in Elbaf. If Noland befriended himself with Giants in the past there shouldn't be any doubt about it.
After we had Vinsmokes in the WCI arc I can up with the idea that Oda will reveal secrets of the EB characters.
- WCI: Sanji -> Vinsmoke
- Wano: Zoro -> Origins (still not cleared, could be both Shimotsuki or Kurozumi, but also another family)
- Elbaf: Usopp -> maybe Montblanc or sth. special about his father
- ???: Nami -> reasoning why Bellmere quit Marine to Safe Nami and Nojiko (might be also tied to Nami sensing any type of weather change)
- Laugh Tale: Luffy -> Joy Boy, meaning of the D.