Ubuntu 13.10 on the desktop will still be shipping an X.Org Server in configurations where Canonical's own Mir Display Server isn't primed. With Ubuntu 13.10 they will likely be shipping X.Org Server 1.14 or version X.Org Server 1.15 if the video driver ABI doesn't break. While Canonical has talked about their next-generation Unity 8 interface, this apparently will be Mir-only. Those running a pure X.Org Server will be limited to the Unity 7.x world.
The Linux kernel likely to ship in Ubuntu 13.10 will be Linux 3.10 or Linux 3.11, but that's up to the Ubuntu kernel team.
The Mesa release to be powering Ubuntu 13.10 will surely be Mesa 9.2 and whatever its latest point release is at that time (or this release may end up being known as Mesa 10.0).
New features being talked about that they will be looking to support from upstream in Ubuntu 13.10 include Radeon UVD video acceleration, Intel VA-API video acceleration, proper AMD Radeon HD 7000/8000 series "RadeonSI" open-source driver support, NVIDIA PRIME, and the upstream X Input pointer barrier support. Most of these new features come from just pulling in the latest upstream code from the Linux community and enabling any necessary compile-time switches. There's also talk of proper touch-screen support and XMir/Mesa changes for Mir.
In terms of Mir usage in Ubuntu 13.10 on the deskotp, "we are going to want to have some mir option." They are also thinking the proprietary (AMD / NVIDIA) graphics drivers will work with Mir if the vendors support the EGL Stream extension. The Canonical developers also admitted that having features like multi-GPU/hybrid support for Mir is a long way out.
For those wanting to watch the discussion in full about general X.Org/Mir plans for Ubuntu 13.10, the video from their virtual meeting is embedded below.