Uhm... I'm not sure it is apt to call realistic constraints an artificial extension of playtime, nor do I think that restricting the amount of things you can carry is the same as forcing you to haul things back to town all the time. That's just your conditioning speaking (or so I guess anyway, as I too feel compelled to collect everything in every RPG I play, like in almost every RPG before it).
When you find the miraculous sword, cast aside your merely astounding sword for some lesser adventurer to find. (Or hang onto that extra sword if you can carry the burden; that one might be worth bringing to a merchant.)
I think I'd like to run into a band of adventurers sporting equipment I have tossed away or ignored. Or perhaps professional scavengers paying to tag along with you and collect what you leave behind, sparing you the senseless looting and tiresome haggling, yet boosting your income.
But more important to immersion it is... that barrels store barrely stuff (perishables, liquids and such) and chests store chesty stuff (here goes gold). Weapons can be found on dead adventurers, or in more or less suitable furniture (dagger stabbed into table, club crammed into cabinet).
Also... Unlimited inventory in a world of fully interactive items? "He's got the whole world - in his hands. He's got the..."
I would not want the cheap trick of limited inventory, but I would like a game that makes it clear that you don't need to pick up even 10% of what you find (arbitrary percentage, assumes extreme amount of things found), and which lets you get away with not picking up anything you don't have an actual use for.
