It depends on how you define innocent. Its true kid does not care about killing civilians apparently however law is not a saint at all. Didn't he send 100 hearts to the marines (I can't recall if he sent pirate or marine hearts) to get his shichibukai position? He is a sort of ally to the strawhats but he is still a sociopath at large.
Law sent the hearts of pirates to the government or Marine, if I recall. For all we know, he could have chosen the bad pirates to take hearts from. However, before the timeskip it was established (can't recall) that Kidd's bounty was the highest out of the Supernovas solely because of how destructive he was. It's also been established that strength either isn't taken into consideration or isn't the only thing taken into consideration, and considering what Luffy has done and will do, I can easily see the crew's bounty raising. More specifically, the trio's bounty increasing since they'd likely be at the front line.
If bounty was based on strength, then I'd think Zoro, Sanji, and Luffy would have similar amount rather than a substantial difference.
Well, within what range of time do you think the monster trio could hit the milestone you mention and what bounty ranges would that include? I don't think any of your posts mention that so far.
I think it could take at least two arcs for that to happen. I'm not sure what the future will hold, but if the crew beat Doflamingo and his crew, I can see the bounty increasing a lot. Not to show how dangerous the Mugiwaras are but possibly out of revenge and spite. Luffy first got bounty placed on him because of the Marine who got pissed off at being owned. Considering how important Doflamingo is, and possibly the influence of the Yonkou who rely on him, I can see the Mugiwara's bounty increasing a lot.
Of course, it depends on what happens. The crew's bounty may not increase much, if at all, if they're thought to have nothing to do with Doflamingo's downfall (IF) or if Fujitora does nothing.
The 2 billion number seems a tad extreme. Dragon is definitely the most wanted but considering the manga has made the point that even going further than 300 mil is hard and the highest we have seen is 550 from a powerful crewmember of WB's the number seems almost absurd. Considering ace and his position it would be hard to believe even WB himself having 3 times that number. In a extreme case I don't see bounties ever crossing the 1.5 billion mark although I expect yonko to actually be around the 1 billion mark.
I dunno - if Whitebeard's crew member had the bounty of 550mil, imagine Whitebeard's bounty. He was a pirate for over thirty, forty years, sailing with a crew and then forming his own crew, which clashed with Roger's many times. Not to mention how dangerous Dragon is to the government and what he's currently doing. I can see the government/Marine charging a high bounty on both of their heads based on what they have done, are doing, and can do. It'd certainly make people want to kill both of them, no?
I think it would be extremely rare to see bounties cross 1.5 billion, but it's not impossible either.