I don't recall there being any mention of inventory space limits and I'm guessing there won't be, but inventory weight is definitely in, in the E3 video you can actually see the weight, both the player's maximum carry weight and the weight of items, shown when the inventory screen is shown. And what I read in the fan interview is that with strength gone, it's now determined by stamina. As for whether saddlebags are in, how could we know this? Nothing has been said about it one way or another, but it's certainly possible that Bethesda saw the saddle bags mod and thought "This would be a good thing to put in our game."
And I think it's pretty obvious that trading will be in, but we don't know at this time how it's handled, I'm guessing that mercantile is merged with speechcraft, but how it actually works waits to be seen. Is it like in past games where you can actually choose how much you want to haggle? Or is it just like in Fallout 3 where raising the appropriate skill simply makes your prices automatically higher? I'm sort of hoping for the former as while the latter approach was more straight forward and involved less hassle, estimating how much lower or higher you can make the price before NPCs will refuse the offer added another small challenge to past games which Fallout 3 and New Vegas lacked.
DIT: To answer the OP, the backlash against the way they handled it in Oblivion was really, really bad. In Fallout 3 we saw a system that was similar to both the first two Fallout games and Morrowind. If they're not stupid or insane they'll realize what a terrible mistake Oblivion's system was and return to form.
And how exactly is Fallout 3 more like Morrowind in this area? And for that matter, what exactly was the way Oblivion handled it that produced this "really, really bad" backlash I don't seem to be aware of? If you want to make a point, then you should explain it if it's not immediately clear what you mean.