VALVE has filed an all new controller patent featuring swappable parts. Not much is known past this new patent but maybe VALVE has something in mind for a future console.
The description states the following for the patent:
Described herein are, among other things, handheld controllers that include housing having one or more receiver portions for detachably coupling to one or more controls. For example, a housing of one such controller may include, on a front surface of the housing, a receiver that is configured to detachably couple to one or more joysticks, one or more D-pads, one or more track pads, one or more buttons, and/or the like. In some instances, a user may swap a first control for a second control based on a current application (e.g. game title) that the user is playing, based on comfort for the user and/or for any other reason. It would be VERY interesting if something pans out regarding this news. Who knows, maybe they want to make VALVE controllers available for next gen systems…
We will see. You can still purchase the current STEAM controller below:

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