I don't see that happening unless it sprouts unprecedented crazy legs for an MCU sequel and (or even first film) and does $500m+ domestic.
$850m WW is a more likely target. Best case scenario is I think $900m. Worst - $800m.
It did $123.8m O/S this w/e and even with a 2.5 multiplier off that (hard with more than one third of that coming from China where the multiple for current US blockbuster sequels skews closer to 2) that's another $184.5m + $282.6m which = $467m + Japan ($10-20m) = $477-$497 O/S + $350-380m Dom = $827-877m WW.
I think you made a few mistkes in your calculations. A 2.5 multiplier would actually lead to (2.5*123.8) + 282.6 = 592.1M. 10-20M for Japan would lead to 602-612M. (You also added 10-30M for Japan instead of 10-20M.) 350-380 DOM would mean 952-992M WW according to your assumptions.
I think the 2.5 multiplier wouldn't be impossible, but it's seems unlikely.
Comparing to TWS: it had 222M int. at this point in its release (I added 15M for markets including Brazil where it hadn't opened yet). It ended with 454.5M int.. So that's a 2.05 total multiplier from that point. If GotG2 follows the same trend, it would end with 2.05*282.6=579M. If it has the same DOM multiplier as TWS, it gets (2.73*145=) 396M DOM for a total of 975M WW. That is an optimistic number, considering movies with lower opening numbers usually have better legs, and I think it will end closer to 900M. But this shows it's at least possible for this to get close to 1B if it pulls out some great legs. We'll have to wait and see, after next weekend we should have a better idea of where it can end up domestically at least, while OS is always harder to predict.