One of the reasons this doesn’t make too much sense is up until now every rumor about the December 2016 standalone says it’s a Prequel set before A New Hope about a group of bounty hunters who end up stealing the Death Star plans.
That rumor originated from Slashfilm, but they were recently wrong about Simon Kinberg taking over writing on the spin-off. They’ve also made some statements about Lucasfilm’s planned marketing of The Force Awakens (where you’d never see Luke, Han, and Leia in a trailer), and sources say those are also wrong.
So if they’re wrong about the Death Star plans, could this new Boba Fett rumor that Star Wars Underworld heard be true?
“Boba Fett is a mantle. The name, the ship and the armor gets passed down to a successor. That’s how he is brought back for the films and explains the character for later stories. Fett fans are in for a few surprises. They [Disney] get the cult status of the character, so you’re going to see more Boba Fett in the future.”
IF the spin-off is set AFTER Return of the Jedi, this could be a possibility. But if the spin-off involves the Death Star plans and is set before A New Hope, this is 100% false. Lucasfilm explained why last year.