Actually, the past 2 years of Minecraft development were almost completely spent on RAM consumption, renderer efficiency, recreating the renderer with an OpenGL 2.1 shading pipeline, switching from direct drawing to VBO's, creating compatibility with translucent objects, etc.

Since January 2013 they've spent almost the whole time on optimizing the performance.

And the only features they've implemented since where features people wanted really badly or features which came automatically – for example, after adding support for translucent objects they were able to add stained glass with just some few lines of code.