I wouldn't say the betting market is saturated, I mean we can all agree that there are numerous dice sites and the like out there, but how many are actually good? How many actually have a userbase? How many aren't just clones and carbon copies from one another? Once you filter out the shit, you really are left with a few sites that are actually quality.

What defines quality? A few off the top of my head are community, activity, and security. A dice site that really nails it is Primedice. Their chat is active, they have a shitload of people betting, and the site overall looks safe and secure. I seen one guy wager fucking $400k worth of btc on that fucking website. In theory, they made $4k off 1 guy.

But to take this question even further, I do believe bitcoin gambling as a whole is still a growing market and can still be considered at a "niche" level. Reason why I say this is just because I don't see a lot of mainstream coverage about these kind of websites (I see more about CS:GO bets lmao). Take this screencap for example:

http://i68.tinypic.com/2sagw36.png

I took this a few months back comparing with Satoshidice (because all of us know how popular it was back in '14), and you can clearly see there has been a growing interest that has not plateaued yet. This means there is still room for entry before it truly does become saturated. So if you have an interest in starting a casino, the best time would have been 3 years ago, but the next best time is right about now.