I was thinking here of a possibility of what could happen in New Vegas: Since the King was helping The freeside staff, because they go through needs, why he did not cause a rebellion to enter the strip, where they have a "life of luxury"?
If The King gathered every gang, could he bring down the robberies of the gate?

There's no question about the Kings taking down the few securitrons guarding the gate, but he wouldn't want to. Firstly, the King likes his position as the Top Dog of Freeside that's why he's staying. He consistently claims he's the "leader" or King of freeside and The Kings get no arguments from the Van Graffs or the Garretts. Secondly, the three branches of power under house are tribes suited up nicely, similar to The Kings of Freeside. A new addition of a tribe on the strip wouldn't fare well, leading to my next point. Lastly, The Kings forceful integration would be starting a war with Mr.House (considering this is pre courier owned Vegas, because you can RP the ending however you please) and that's starting a war they'd lose. The three tribes would have to betray house in order for there to be a fighting chance, and the Tops won't (Swanks loyalty to House is obvious, if not for loyalty his own personal gain). Mr. House brought the tribes in so they could manage and protect the strip in exchange for the life of luxury. Backtracking, if the coup d'état of Vegas were to happen from NCR, Legion, Tribes or whatever support the Kings ("The Kings" would be the least likely group to get support from groups anyways for different reasons) managed to gather how long until Vegas would end up just another shanty town?

There is no way the King's would win in a war to take over the strip. They would have to fight the NCR, the three tribes and Mr. Houses securitrons who are well geared up. This will only result in them losing and suffering mass casualties even if they had weapons from the Van Graffs.

The Kings didn't present themselves as a group of thugs that just fought for more loots and stuff though. They were just cool guys of Freeside that are taking care of the hood if you know what I mean.

sort of like the old style mafia was before it got into drugs and money it wall all about protecting your fellow brothers and the neighborhood.