Just to put things right: the problem is not with the open source drivers, the issue (when it comes to S3TC) is
software patents. Because of this and other shortcomings of S3TC supporting
ETC2 is mandatory starting OpenGL 4.3 and OpenGL ES 3.0. The same versions also introduce optional support for royalty-free
ASTC. Mesa based open source drivers (intel, radeon, nouveau) will be able to make use of ETC2's predecessor
ETC1 starting with the next Mesa release, if only by means of having th driver convert it, since there is no hardware support.