I do most of my long-form reading on devices that don't have a space key.

I am not talking about fixed pages or clickbait websites where you have to scroll anyway and then click a "Next" button, but about having a flexible way to enable pagination of content.

That pagination is one of the reasons why for me the best way to read something like the stories in http://longreads.com/ is on Instapaper (or a similar tool).