Probably not, to be honest. This game is absolutely huge in terms of file size, and distrubting that ourselves would cost a fortune. Putting demos on Steam actively reduces sales for any game, which is why you don't see those anymore; it gives a prospective buyer a feeling that they aren't doing their dye diligence if they don't play the demo, so they delay buying, sometimes indefinitely.
On the flip side, Steam's refund system, paired with let's plays, user reviews, and professional reviews give players more of a chance to learn about games without a demo than ever before. So as much as I used to be a proponent of demos, to my own surprise I've changed my tune.
But I love he refund policy that lets you get your money back if you don't like it, I have to say. It's equivalent to a demo, except you get the full experience for up to two hours; and it doesn't come with the negative psychological baggage that suppresses sales. People make refunds on our games for a variety of reasons every month, but I'm proud to say we're better than average in the store in people not wanting to. For me, with those people that did take the refund, I'd rather they have their money back and be happy rather than being disgruntled with me.
I know I changed the subject a bit, but the whole industry has really changed since the first game came out, and these are the more current methods that seem to benefit everyone well.