Not many details right now, all we know it's focused on the saiyans as a species, not just goku and vegeta. A throwback to the saiyan origins, or the first super saiyan god maybe.
didnt in the recent interview Toriyama said the real "legendary super saiyan" and "original super saiyan god" is the same? the 6 virtuous Saiyan ritual to active SSG reflects the LSS and his 5 friends.
So, then Goku was given energy from his friends during the fight with Brolly, that kind of mimics the "ritual" for him to attain Super Saiyan God?
You could say that, but that consisted of 4 Saiyans, a human and a Namekian...
That would kind of explain why he didn't turn SSJGod at the time.
At the same time, it also (kind of) eplains why Kefla was so strong fused, without destroying the canon.
But that kind of leaves a few other problems. Like, how do SSJ2 and SSJ3 factor in compared to LSSJ/SSJGod. We know for example, that Goku couldn't do anything against Beerus as SSJ3, but matched him (though Beerus wasn't af full strength) as SSJGod. Does that mean that Brolly was on par with Beerus?
You're putting way too much thought into DBZ, especially in a form/ritual that was conceived almost 20 years after Broly. ---