Currently the multi-function trackpad for Steam comes in two flavours - the SteamVR Gamepad, and the handheld Vive Controllers. But suppose I wanted to make a larger, haptic device that was "ambidextrous" (suitable for both left-handed and right-handed users), designed for PC to replace the functionality of existing trackpads...
Would such a technology collaboration occur with HTC, or Valve?
The Steam controller is designed and manufactured by Valve. The Vive controller is a collaboration between the companies but designed and manufactured by HTC with hardware design collaboration with Valve. You'd probably want to talk to Valve for what you're thinking about doing.
This is actually something you can do independently via Steamwork's Steamtracker program. Basically you'd apply to be a licensee and then would create your hardware to be compatible with SteamVR. Getting it integrated into SteamVR as a native device would require collaboration with Steam and you'd probably have to develop SDKs or plugins for the major gaming engines.
The Vive controller is a collaboration between the companies but designed and manufactured by HTC with hardware design collaboration with Valve. You'd probably want to talk to Valve for what you're thinking about doing.
That was kind of what I expected... besides that, the device is a tactile peripheral just like a normal trackpad, not a mocap-based situation.
As for the Steamtracker program, that is currently very difficult for people who don't live in the USA as, despite others asking them to set up facilities globally, Valve still want you to travel to their studio instead to do their training course which, for me, isn't very practical.