Mesa To Drop Support For Ancient Drivers
Back in 2011 the classic Radeon drivers were removed Adam Jackson of Red Hat is planning to remove the ability for Mesa's current libGL to be able to load DRI1 drivers. This is basically about trying to load old DRI1 drivers from Mesa pre-8.0 onto a system with the current Mesa libGL loader. Mesa has retained this ability for being able to load these classic DRI1 drivers but nearly nine years after old driver code was dropped from Mesa, phasing out this ability to load DRI1 drivers is now planned.
Mesa developers aren't aware of any Linux distribution itself offering such an ability and RHEL6 was the last time such a driver combination was even attempted. A Meson build system change is currently pending for allowing parallel Mesa installs in making use of GLVND (the OpenGL Vendor Neutral Dispatch Library). So with that change it would still be possible to load DRI1 drivers on a modern system should you really want to, just some extra steps involved.
Those remotely interested still in DRI1 drivers can see this mailing list post for all the details.