There is a lot of speculation about what sorts of things Blizzard will do next in Diablo 3. They regularly talk about PVP as a thing they want to do but it is pretty clear that is a long term goal that may never materialize. I tried a little bit of random PVP in the arena and it was hilarious, bloody, and over in two seconds at most. While I am sure we both could have built ourselves for toughness instead of being glass cannon PVE builds it is fairly easy to imagine a Witch Doctor build with the full Jade Harvester set that does 20,000% weapon damage in the first ~2 seconds of the fight while being invincible. (Spirit Walk/Haunt/Soul Harvest). This would do ten times as much damage as my character can take, and I am built reasonably tough. So I really don't see PVP as anything more than a silly sideline like it is right now.
What is interesting is that they are wanting to create more challenges for people and they intend to do so with Ladder Seasons and Tiered Rifts. I love the idea of ladder seasons where people can play in a fresh new environment to compete to be the first to various benchmarks in the game but they plan to put special gear in the ladder that you can't get outside it. I don't want to play new characters myself - I want to play my main, and not being able to get the gear for him would be irritating. Restarting has its own appeal but more than anything I just want to get better on the one toon and I tried making alts to optimally farm gear for my main in D3 at launch and I *don't* want to do it again.
The solution I would use is to have special gear for ladder seasons and when that season ends and all the characters are integrated into the general pool make the gear that dropped in that ladder now drop for everyone and make up a new set of special gear for the next ladder season. This would mean that ladder players have an interesting advantage in that they get first crack at new stuff and new seasons will see new innovation but if you really want to maximize your character you can just wait and eventually everything will be available to you. This would mean that Blizzard would need to design an awful lot of new gear all the time but I think that is a great thing and would keep people interested and character designs shifting. I like that.
I had an idea for a new thing to do which was a rift that essentially was a To The Death sort of thing. You would appear in a random area with mobs constantly spawning that got harder and harder and the more you killed the better your rewards. However, if you ever die or leave the area you cannot return. The idea would be to really offer a reward for being powerful and never dying. The Tiered Rift thing seems to be their version of that - you get tokens for completing rifts and then you can cash in those tokens to do harder and harder rifts with bigger rewards. It seems like they want to reward both clear speed and ability to kill really tough things. This could work out great, depending on the implementation.
Obviously they also just need to add more things to the game. There are an awful lot of unfortunate legendary items out there that aren't very interesting and I think they would do well to put a bit of effort in to make they cool. A lot of the really neat effects require quite a bit of work but some would be incredibly easy - if Hammer Jammers started with 1000 vitality I would actually have to consider wearing them instead of instantly vendoring them and this sort of change is very easy to implement technically.
Still having tons of fun though, and very much a fan of loot 2.0. The AH will not be missed.