Is there really a saturation point for information? That would mean that we have discovered all there is to know about our entire universe. Is that possible?
I would think that niches in scientific research, astronomy and space travel would resist saturation the best. But I have noticed some untapped potential in the sewing niche that hasn't been touched yet. That one might be hard to go after. There is also untapped potential in the children's toys niche.
Honestly, all you need is a new take on a subject. Certain niches attract certain demographics, and if you can cross demographic lines, you may find yourself with a unique take on an oversaturated niche. In theory there are unlimited versions of the human brain possible in unlimited positions on our planet, so there is theoretically unlimited takes.
Basically, you need to be better than the competition, regardless of niche size. JavaScript tutorials is a huge niche, but Fireship.io is the best - and thus he gets all the subscribers. Chess is a huge niche, but GothamChess is the winner. The reason why is those two produce entertaining content in boring niches, so they rise to the top.
You also have to ask yourself what your competition is doing wrong, and then do the opposite. Mark Manson is another example. The self-help industry is a rosy pump-up rally that is disconnected from the realities of life. Mark Manson is a more realistic and downright pessimistic approach that includes profanity. But he runs a successful blog. Yes, the self-help industry is oversaturated - with positive pump up stuff from Zig Ziglar and Tamara Lowe. Everybody is going the same direction - and you go the opposite. You do it better, faster, stronger. And then you win.