Mesa's DRI3 Support For EGL Still Baking, The State Of DRI3 For X.Org Drivers
Mesa right now only supports DRI3 with GLX, but Martin and others have been working on DRI3 EGL support. This patch series made up of seven patches provide the working DRI3 support for EGL.
The Intel DDX driver has long supplied DRI3 support, but last November was disabled by default as the DRI3 code within external libraries was buggy and causing X.Org Server crashes and lock-ups. Enabling DRI3 in Intel right now with the latest xf86-video-intel still requires setting the --enable-dri3 build-time switch. The xf86-video-ati DDX for Radeon hardware support has offered DRI3 support since earlier this year but requires Option "DRI3" to be set in the xorg.conf. The newer branches of the xf86-video-amdgpu DDX also have DRI3 support. The xf86-video-nouveau DDX driver enables DRI3 support only when GLAMOR acceleration is used while DRI2 is the default for EXA acceleration. However, via the DRI option in the Xorg configuration, DRI3 with EXA can be specified. XWayland also has DRI3 support.
As far as I am aware, DRI3 should be in good shape with the X.Org Server 1.17 series and newer. DRI3 is designed to improve security, improve window resizing, and offer other benefits.