AMDGPU DAL/DC - What immediately comes to mind when thinking of "missing features of Linux 4.10" is definitely AMD's DAL/DC display code rework for their AMDGPU DRM driver. This is the long-in-development rework to their display code. This huge rework is needed for supporting future hardware, enabling HDMI 2.0 display features, supporting atomic mode-setting, and a lot of other modern display features. Why it's a big issue for me is that there isn't any DP/HDMI audio support with AMDGPU until this lands. That will be a big issue for those wanting to use a modern Radeon GPU in an HTPC (and not use AMDGPU-PRO) or if you are using just your monitor's speakers and relying upon HDMI or DisplayPort. I'm in that boat with nearly all of my test systems these days just using HDMI/DP audio. DC isn't coming for Linux 4.11 either but Linux 4.12 at the possible earliest for mainline.
GeForce GTX 1000 Series Nouveau Acceleration - Another big annoyance to me is that there isn't any hardware accelerated support yet for the GeForce GTX 1050/1060/1070/1080 "Pascal" GPUs with Nouveau. This isn't due to the Nouveau developers but rather NVIDIA not yet releasing the signed firmware images needed for enabling accelerated support. It doesn't look like the Pascal 3D support on the consumer cards will be sorted out until at least Linux 4.12.
Better Nouveau Re-Clocking - Another big Nouveau wish list item by myself and others is seeing proper re-clocking support in this open-source NVIDIA driver. Better re-clocking would definitely help Nouveau on the performance front. Nouveau Linux 4.10 code does bring boost support for Kepler / Maxwell 1, but some items still not found with this community-written driver include: automatic re-clocking with all adjusting of performance/power states needing to be done manually right now, Maxwell 2 re-clocking isn't yet working mainline, and obviously no Pascal re-clocking yet and that may take a while longer past the point of seeing the 3D / signed firmware support. Re-clocking is made trickier with the GeForce GTX 900 series and newer due to the signed firmware situation and restrictions around the PMU.
Radeon Vega Support - And another graphics item since you are reading Phoronix after all... With Linux 4.10 there isn't yet any support for AMD's upcoming high-performance "Vega" graphics processor. Vega support as well is blocked on the DC (DAL) code needing to land. So we won't see Vega until probably Linux 4.12 at least. Vega is still supposed to launch H1'2017. If AMD developers would have been able to get Vega support in Linux 4.10 it would have rolled out to more distributions sooner and provided for a better out-of-the-box experience when new Radeon Linux gamers upgrade. With the way things are looking now, on launch-day the fully open Vega Linux driver support will probably just be available in patch form -- or of course using AMDGPU-PRO if not wanting to roll your own kernel and Mesa.
Clang'ing The Linux Kernel - It's still not possible to build a fully-mainline Linux kernel using the LLVM Clang compiler. There continues to be the Linux Foundation project site covering this organized effort. But there hasn't been too much work in this direction recently for getting the remaining changes into the Linux kernel or Clang for allowing this feat to happen. At last check, the developers involved were preoccupied with other work.
Reiser4 - While mentioning Reiser4 quickly deteriorates into talk about its former developer and convicted murderer Hans Reiser, there still is a dedicated group continuing to work on Reiser4. Out-of-tree patches continue to be maintained for Reiser4 with new kernel releases and the occasional new features. But there isn't any major company backing Reiser4 and thus we probably won't see it mainlined anytime soon if ever.
Bcachefs - Bcachefs has been promising and for offering next-gen features and some even arguing it's better than Btrfs or ZFS. The current state can be found via this project page but it's not yet mainlined in Linux.
MuQSS - The MuQSS CPU scheduler has been promising and is the evolved solution from the BFS scheduler. MuQSS is showing much promise but it's unlikely Con Kolivas will pursue the effort of trying to get it accepted upstream.
Bufferbloat / Make WiFi Fast - While some work has been merged in recent kernels, there is still outstanding work on reducing buffer-bloat as well as improving Linux WiFi/wireless performance. More details on these efforts via BufferBloat.net.
BUS1 - BUS1 as the spiritual successor to KDBUS remains in-development as a modern in-kernel IPC mechanism. We might see it ready and acceptable to developers for getting into a kernel release later this year, but it's not found in the mainline Linux 4.10 kernel.
Are there any other features you would have enjoyed seeing in Linux 4.10? Share your thoughts with us this weekend in the Phoronix Forums.