Valve is rather secretive about all its comings and goings - that's why some are still waiting on that Half Life 3 news - but we do occasionally find things out from changes it makes to the Steam platform. In the case of its VR controller support, it looks like Valve might be looking to make a new prototype controller available for a wider audience, as it's added support for a new prototype controller.
The likelyhood is that this is the same prototype controller - or a tweaked version - that we saw earlier this year at the Steam DevDays. More like the Oculus Touch controllers, these modified, slimmed down version of the Vive's wand controllers sit in and on the hand, making it so you can grasp and let go, without losing touch with the gaming world. Your hands remain tracked, but you can pick up items as you would in the real world and let them go again when you want, without your controllers hitting the floor, or dangling in a silly manner from wrist straps.
There's no hard evidence that that is exactly what we're talking about with the new Steam prototype controller support, but it's very possible.
This could well be Valve's way of preparing its Steam software for a wider devkit availability.
What do you guys think?