I've been working on an alternative method of implementing good mouse accel at the driver stage that doesn't require test mode or paying a lot of money for an EV code signing certificate. I discovered a driver/library called Interception which enables such a thing to happen.
Interception installs 2 upper filter drivers (keyboard.sys and mouse.sys, fully signed) for kbdclass and mouclass devices, which allows user-mode applications (which have no signing requirement) to manipulate keyboard/mouse events at the driver level. I wrote a very simple console application which interfaces with the interception mouse filter driver and applies the quake live accel algorithm.
Kovaak (author of the amazing GUI for my previous kernel mode filter driver) has updated his GUI to support this new method. He has also started up a blog about mouse acceleration for gaming, which includes information and downloads for accel driver related things. Here's a link to this new /!\ TEST /!\ version.
Kovaak has some concerns about this interception library triggering anti-cheat scanners. There is certainly no guarantee that anything is safe from triggering VAC, but logically this new method is significantly less 'dodgy' than the previous driver which to my knowledge never triggered any anti-cheat. Use at your own risk. Also the source is provided so check it out if you want.