I think open world in star wars is about due myself. as for the content I think the game should indeed be centered around Boba Fett, but for more of a balanced reason. Most of the games we have seen up to date have been Jedi or Sith based like the Force unleashed, I think stepping away from that would be a great step in the right direction at least for a little while.
Now about the game, if it's open world then the game has to feature more than 5 worlds, it's star wars and so I would for as many worlds as they can, don't forget these worlds might only have a small area compared to others, with major worlds having the more expanded areas.
It would also have to have a great story, not just be a shooter. I feel like most games today aren't as thought out as they should be, we complete them to quickly and then get bored. I prefer games that take a good while to complete, if Disney has the resources then why not put it to use? Have a sizable team working on the environments, a second on the story missions, and extras and a third on the character models, and in game items.
And it better be done by a company that is NOT EA! they ruin everything they touch.