My guess, based on what I've seen, is that 5e is going to follow the more-or-less-standard "XP value of defeated monsters/hazards by CR, modified by circumstance, with optional quest XP" model. It's relatively easy to calculate, relatively easy to grasp, and works reasonably well.
Neverless, tinkerer that I am, I can't help but wonder if it's the best tool for the job. I have heard it posited that "XP value for monsters" leads to kill-happy adventurers, who envision every creature that lurks in the dungeon as a giant piñata that they should just smash and have XP come raining out. The archetypal example is the paladin slaughtering baby kobolds because "They aren't worth any XP alive."
The earliest editions of D&D used a different model, in which you gained as much if not more XP based on the value of treasure you looted than the monsters slain. After all, in those early dungeon-crawling days, the acquisition of loot was the story: that's how you "beat" the dungeon, by collecting all the goodies and getting out alive. (The lore goes that you also didn't bother to name your character until 3rd level, because 1st and 2nd level characters were so fragile that they were likely to die before they got that high and there was no point in getting attached. I don't know if I buy this as the "norm," although I have no doubt it was true in some groups.)
Since monster difficulty was all over the map and traps tended to be "You chose... poorly. Roll a new character..." in nature, the high XP reward of treasure vs. monster-killin' made stealthy filching, swindling monsters, and engaging in parley much more attractive options. One forum poster described being forced into combat as "the failure state" in early editions, which I think is an overstatement, but not too big of one.
In later editions, as the spinning of heroic tales began to take more focus over the tapping of 10' poles to set off traps as you walked down the dungeon corridor, people began looking for alternative means of character advancement. Alternative games on the market began doing things like giving awards for "good roleplaying" or "advancing the story" or even just "XX per session." I remember being baffled by the original Traveller because there really was no character advancement: once you mustered out in the character generation process, you were pretty much set in stone. (Technically, there were training rules, but the game hated you for wanting them. My memory is that it took a year in-game and a ton of money to get 1 pip in anything. But it also had a 2d6-based resolution mechanic, so 1 pip was a big deal.)
"Killing monsters" kinda became D&D's version of "advancing the story." In actual play, my group in the early days didn't usually bother with awarding XP for treasure, and didn't bother with training to level-up, which meant that we killed a lot more monsters to advance than a RAW group would have. But because monsters had treasure, and there were no "magic item shops" to be found, we ended up with characters carrying around thousands of gold pieces (in bags of holding, natch) and having nothing to spend them on.
At the time we (or at least I) blamed this on the game, but that's like the people who put fines on "Free Parking" and don't auction properties in Monopoly and then complain that the game lasts forever. It's not a failure of the game system if you're doing it wrong. :P It miiiiight be a failure of the game writer to be transparent about how the rules work and why... just sayin'. Everyone knows that the esteemed E. Gary Gygax was a clear and straightforward writer. For realz.
Anyway! The point of all this rumination is that I'm pondering what XP award method I should use for this 5e game I'm planning to run. I have an experienced group of players who are all fairly set in their gaming ways, so it's not like I have to use XP awards to "train" them in certain behaviors; I'm tempted to say "screw it" and just announce periodically "Well done! Level up." at the end of a session or when appropriate to do so. But in a sandboxy, flat-progression system like 5e, what even is "appropriate" for leveling any more? Content isn't gated by level anywhere near as strongly as it used to be, so you don't have to "Make sure the party is at least X level before they attempt this dungeon." Besides, getting XP is fun, like getting the payout when you put a coin in a slot machine. It also makes a nice benchmark to measure the challenge the group faced: "Holy cow, 1200 XP, what a session that was!"
5e is designed to fast-forward you through levels 1 and 2, and then coast from 3+. The only reasons 1st and 2nd level exist, it seems, is to make it easier for new players to create characters without having to make too many choices and learn too many abilities right out of the gate. In fact, online advice from the designers has been for experienced groups to start the campaign at 3rd level and skip the rats-in-the-basement session all together. I'm starting this particular game at 1st, because 5e is new to us all, but I can see what they're getting at.
I think that while we're going through the Starter Set at least, I'll probably just end up using the suggested XP awards and rolling with it. By the time we get through everything in there, I imagine the DMG will be out, and I'll re-examine the issue based on what it says in there. But in the meantime, players, if you have any input, I'd love to hear it. :)