Season Six Spoilers
I can't reveal my sources. Take this as you will.
The Monarch will become the new Sovereign. This is why Killinger told him he was not to be on the council of twelve.
The business and building in New York left to Rusty by JJ is actually Impossible Industries, which Sally was given in the divorce but allowed Richard to continue running/living in out of pity.
Rusty will get contracts, via the business, with the OSI and thus go head to head with The Monarch (Via Rusty's being arched and via the OSI projects) like "So much butterfly themed Romulus and Remus".
Speaking of which, and we all saw this coming, The Monarch is Rusty's half brother, revealed this season, and bringing full circle the title of the series.
This familial relationship, however, has nothing to do with the Monarch's motivation for hating Rusty. This hatred comes from Rusty inadvertently killing the Monarch's father. Due to confusion of the situation the Monarch has always believed Rusty did it purposefully after finding out that Monarch's mother might be his "New Mommy" after seeing Jonas and her together at one of his swinger's parties.
And I can also confirm that the popular theory is true, Vendata is The Monarch's father. This ad the above explain why he tried to strangle Rusty, thus having the Venturion project cancelled.
Again, take these as you will.