In reply to Norris.

The fact that Jetpack has 1m installs doesn't mean that 1m people installed Jetpack due to custom CSS. Same goes for W.com - 50% of the sites, doesn't mean that they all are paying for Custom CSS.

And yes - themes provide custom CSS options ( I do too ), and plugins do that as well. Which is why I don't think that this is a direction the core should be moving. WordPress is a flexible, extendable platform. The purpose of a plugin is to add functionality that some users might require. That sounds like a perfect fit for Custom CSS.

Using analytics like "1m people want X and Y" to add features to Core can quickly go down a rabbit hole. Have a look at popular plugins - tons of things to add to core - Google Analytics, Regenerate Thumbnails, etc.

When you're saying "easier for users" you mean "easier for advanced users". For people who don't know what CSS is - this is just another item in the menu they don't understand.