Eric Anholt has added the new DRI loader entry point to the X.Org Server GLX in order to support future Mesa drivers in the "mega driver" configuration. DRI drivers will change to this new entry point once the mega driver patch series lands and to eventually transition all drivers to the new interface.
The Mesa patch series hasn't landed yet, but Eric has now got his change committed to X.Org Server master and is hoping the small patch will also be back-ported to older versions of the X.Org Server to ease adoption.
Mesa mega drivers will allow for reduced size of the compiled libraries, allow for potentially more compiler/linker optimizations to enhance performance, and will expose less public symbols. It's not known when the mega driver patch series will land, but it may end up being postponed until after the Mesa 10.0 release so this xorg-server patch can be more widely adopted in released versions of the server.
The new DRI loader entry point is supported by the X.Org Server with this Git commit.