Why would you want a 360 pad replacement
There was a lot of hype over the Steam controller and how it would be be a step up from a dual analog gamepad, just not quite as good as a keyboard/mouse.
Which was probably quite misguided. We heard very early on, from the beta impressions, that many people were struggling with it in many situations. The defenders always claimed, "People just need to get used to it!", but I think that is also misguided and merely wishful thinking. It isn't like learning some new controller like when the first single or dual analog stick controllers came out and it was just a matter of learning the coordination. People have been saying the Steam controller simply isn't accurate enough in certain situations and simply doesn't feel good in certain games.
People are also now saying that it just needs to be configured properly, somehow assuming that because there's a ton of available options, that there will somehow be some magical 'right' configuration that erases all bad feeling or whatever.
From what I'm gathering, I think people should give up thinking this will be useful for most games that require fast and accurate input. You can probably do one or the other(fast but not accurate and accurate but not fast), but not both. I'm sure we'll see some freaks out there that show that it *can* be done and people will use these as examples that there's nothing wrong with the controller, but I've also seen people use a gamepad to put in elite lap times in Project Cars, even though I think it's well established that gamepads just dont work very well with the game overall. They will be exceptions and outliers, not evidence that it's just a matter of time.
Basically, dont treat this as a replacement for either a 360 pad or a keyboard/mouse completely. Both of these things will still have their place, whereas the Steam controller will have a bit of overlap of both depending on the title while also providing its own unique functionality at times.