This thought has been bouncing around in my head for weeks, so I might as well get it out.
I'm pretty sure that Raiders was suppose to be one of the factions you can play as. Fallout 4 has all been about the factions. The Minutemen, The BOS, The Railroad, and the Institute. It's one of the classic aspects of the game, and Fallout 4 took it further by allowing you to every major factions in the game... accept the Raiders that is. However, I think being able to join the raiders was part of the plan.
We all know at this point that the Combat Zone was suppose to be much more than a simple dungeon with a companion as a reward for clearing it. You were suppose to be able to watch fights, place bets, and actually take part yourself. BUT There is also Easy City Downs. It's a race track, but for robots in lue of horses. Easy City Downs is very similar. You walk in, see something cool happening and want to take part only for everyone to attack you. What's strange is your companions talk as if it's possible to actually participate, by recommending who to place bets on, that you sit down and watch, ect.
So far, we've got two of these. Raider controlled areas that evidence heavily suggests should have been much more than what they ended up being in the end product. The prevailing theory is that these individual pieces were cut for time, but what if they're something more going on? What if these were part of a much large unfinished raider faction you were suppose to be able to join? It seems at least plausible to me.