Eagle is a small loader for DRI drivers to use EGL, the Khronos interface for between their APIs (OpenGL, OpenVG, etc...) and the underlying window system. Eagle actually began while Kristian was working on DRI2, but then along came Wayland and it found a use there too. At the same time there is already a EGL loader within Mesa, but it's not ideal and currently will just work with Gallium3D drivers.
Kristian, however, on his blog has talked about The Eagle EGL Loader and merging that into Mesa. By doing so, Kristian describes the benefits of Eagle going into Mesa as allowing it to learn to load DRI2 drivers and there will be just one EGL loader for Mesa. If this code ends up being merged into Mesa, Eagle though will live on as Kristian wants to continue to use it to experiment with integrating EGL and GEM/DRM.
Also learned in this blog post is that Kristian intends to write a Eagle+KMS back-end for the Clutter tool-kit, so that applications using Clutter could run directly atop the KMS frame-buffer. There is also a Clutter-based Wayland Compositor under development too.