With the EV3 kit, Steam has revamped the triggers for improved reliability, re-calibrated the grip force sensor to improve consistency, and recessed the system and USB buttons to avoid accidental presses and improve charge cable access. Improvements have also been made to the strap, LED lighting and fit and finish.
Unlike the EV2 controller, which saw a significant design revamp, the latest kit is more about perfecting the product -- a pretty good sign that Valve is getting it ready for a consumer release. The company also noted that "EV3 kits are being produced in much grater quantities than EV2," which only shipped to several hundred developers.
Valve is ready to send the EV3 kit to new testers and current EV2 developers -- you can apply by filling in an online form that's set to go live "soon." There's still some testing and tweaking likely after that, but if all goes well, hopefully you'll be able to start grasping, squeezing and shooting in VR with Knuckles sometime in 2019.