I've heard unfounded speculation that the steam marketplace is a precursor to selling your games (and Steam taking a piece of the pie). Could get interesting if it happened.

I personally highly doubt that's their intention with the marketplace, and I certainly hope they don't. They'd basically turn into a virtual Gamestop. Don't need more of that. Besides, I think they'd loose developer/publisher support in a heartbeat.

It could be that publisher would be getting piece of the pie (transaction fee) too, and there might be restrictions on how many times one license can be resold etc. I thought XBone was originally going to get a system like this before they ditched it, but then there we are still talking about physical retail games.

But considering how relatively new AAA titles are sold for mere few bucks or PWYW Humble Bundles, I don't see that much point adding such a convoluted extra system on top of the current one. There may be certain cases where it sounds a good idea (e.g. you buy an expensive game you end up hating, or which doesn't work at all on your computer), but most of the time it doesn't sound that useful.

Here's a new thought. How about we think of digital games as tattoos?

That short singleplayer game which was excellent but has no replay value, is the hilarious tattoo reading "All your base are belong to us", which you don't show off anymore, because it really isn't as funny in the long term as you thought it was when you had it made.

That one game you really regret purchasing because it turned out to be completely different from what you expected, is that tattoo of a couple of Chinese characters which you thought meant "eternal bravery", but later turned out to actually mean "chicken soup".

That game you keep going back to over and over again because it's just so awesome is the tattoo of the name and birth date of your child, adorning your upper arm.

Regardless, you won't be able to resell any of them, or for that matter lend them to others (Ouch!).