ETC2 is very interesting for OpenGL and is in a much better legal state than S3TC. With OpenGL ES 3.0 from this summer, ETC2 is now mandated and so it's adoption should begin to take off. With Intel wanting OpenGL ES 3.0 in Mesa by early 2013, ETC2 support had to come sooner rather than later.
Intel has been working on ETC2 Mesa patches for several weeks but only today the support was merged to mainline Mesa. Ian Romanick committed the patches enabling ETC2, but for now it's only supported with Intel graphics hardware.
From the commit:
This patch enables support for ETC2 compressed textures on all intel hardware. At present, ETC2 texture decoding is not available on intel hardware. So, compressed ETC2 texture data is decoded in software and stored in a suitable uncompressed MESA_FORMAT at the time of glCompressedTexImage2D. Currently, ETC2 formats are only exposed in OpenGL ES 3.0.