By the way, how does people reacted here when Akainu got 5b bounty?
The usual: the haters coped that the bounty was wrong, not true, etc.; the others were happy or surprised.
I was happy, but not surprised since I have always believed it was 5. Other than Akainu's own relevance, there was a crystal clear auto-quote of Oda to Doflamingo's star system, which had 4 four-star bounties and 1 five star bounty.
Not to mention, no bounty system ends at four lol. It's either 5 or 10.
And again, even Yonkou's bounties have the 5B range as the max.
In short, It was very much hinted.