Yours truly, writing at Nice Web Type:
When a responsive composition meets a viewport, there are different ways to fill space. What interests me most here is a fundamental triadic relationship in typesetting — that of a text’s font size, line height, and line length. Adjusting any one of these elements without also adjusting the others is a recipe for uncomfortable reading, which is one reason designers have such a difficult time with fluid web layout.
What we need is a fluid way to set line height. Web designers should be able to define line height as a range, like we do with min- and max-width.
Since I wrote that, several folks have published scripts that actually do it. Mat Marquis and Jim Jeffers each took a crack at a jQuery plugin, and more recently Viljami Salminen made a version that doesn’t depend on jQuery. Viljami’s animated gif says it all. I really like where he’s taking this: supports multiple instances, tested in lots of browsers, and performance is great.