The latest Android distribution numbers are out and they show that Marshmallow use is growing. It's only at 2.3 percent but that's a jump over last month's 1.2 percent in use. This is very low, especially considering Android N was released to developers this week
Google released the first preview version of Android N to developers this week. It shows better notifications and customization, among a lot of other improvements over Marshmallow. You must be a developer to download Android N, but without verification of that anyone can claim to be one and get it.