Good theory. Personally I would say it's way to high because Sanji has always been about 25-35 % of Luffys bounty so if Sanji has 3.2 then Luffy would have to be at 10-12 B... But how about 2.325.900.000 with Luffy being 6.560.560.000 (gomu gomu).
(Zoro placing in between them, 3.6-4.0. Above Mihawk)
Like I said above, Japanese people have a thing for puns. There are some significant/insignificant digits here and there but I think Oda would give puns to more important characters for endgame stuff imo.
I don't feel Oda will put sanji's bounty anywhere lower than that of mihawk
Sanji will be the man who will be most feared by marines, and sanji's bounty also very much depends on luffy's achievements
So 3.6 to 4 bil is my guess
Yes he told that to Kuma in TB. In the meantime after 15 years irl and 2+ years in the verse he's done shit. His best eos fight will be an Admiral if he's lucky and Oda wont have Law/Kidd fighting them. If he is lucky he will get some 3.2B only with name puns, if we go only by feats he doesnt deserve to pass 3B line.