How important is predictability to you?
My Bartle-type is heavily on the Explorer side, followed by Killer and Roleplayer, with very little Achievement thrown in. So, not surprisingly, my favorite games have been those with much freedom of movement, much freedom of choice, and a lot of surprises (both harmful and beneficial to my character). Diablo 2, Star Wars: Battlefront, Mario Kart (SNES)...these are some of my favorite games of my 20+ years as a gamer. So I'm very interested in an RPG that offers more control over the character's responses to experiences than control over the experiences themselves.
I think there are a lot of gamers like me (though most probably aren't as self-analytical as I am, and so they might not be able to define themselves as such a gamer). Those are some of the most popular games in the history of the industry.
Think back to Monopoly. The first time playing, perhaps you knew that some of the cards were good for you and some were bad, but you probably didn't expect the particulars, like "There was a mistake in your tax return. Pay the government $500". Ouch! That 500 bucks may have been the difference between being able to afford Park Place and having to mortgage Boardwalk. And who knows how the dice will roll? These unpredictable game elements aren't minor...they're the difference between biting the dust and puting your fellow players to shame.
So how could a similar unpredictability be applied to RPGs?
We could start by eliminating experience points as a guarantee for killing, as I suggested in Green's latest blog. Experience-rewarded kills are a major source of predictability in most RPGs. Over the past 20 years or so, a gaming culture has developed that is very mechanical and grind-oriented. Merely providing alternative ways to gain xp isn't going to dissuade players from grinding, and something else will become the grind if you just shift the optimal xp expediency toward some other source.
I'd like to see an RPG in which player progression is largely dependent on chance, as it is in Monopoly. In Monopoly, the dice decide what you encounter and the player decides how to respond and plan ahead. You may prefer Boardwalk and Park Place to every other property set, but you never happen to land on them to buy or you never happen to have the money when you do land there.
Now imagine an RPG in which skills/spells and equipment usually aren't acquired by going to a foreknown location and paying your dues. Instead, you wander wherever interests you and happen into encounters (people, places, things) that provide you with an opportunity to acquire something. Like in Monopoly, you decide whether to use your limited resources (some are universal currency, others are situational...like having what the NPC wants) to acquire the thing offered, or whether to hold onto that currency for the possibility of other objects.
In Monopoly, sometimes you passed up an offer you wish you hadn't, yet still had fun...and that would be possible here. What makes it possible is that your property still has regular "live" value, that it still has trade value, and that it has situational advantages. In Monopoly, the situational advantage is relatively unpredictable...your opponent just happens to keep landing on your property and having to pay you. Likewise, in an RPG, your weapon might be just so-so most of the time, but it proves to be the bane of a particular genre of creatures. For one example, think of Bilbo's sword Sting and how he only realized its magic when in the appropriate circumstances.
This system could be used to reward player knowledge, "lore" skills and encounters with wisemen/scholars by hiding an item's identity until researched, if not used. If applied to objects such as spells, there's a lot of unique fun possible. Imagine finding a scroll that seems to be some sort of transfiguration spell, but you're not sure what specifically it does. Without acquiring clarification, you have the option of taking a gamble by using it blindly, or on limited information. So perhaps you use this scroll, which bears a vague sketch of some four-legged creature, and your character is temporarily transformed into a small dog with little defense...or perhaps it changes you into a terrifying beast half the size of a cottage. Either way, you're surprised and a very engaging experience may follow (you have to run like hell or you wade through your enemies like water). Or you may cast it on yourself and nothing happens...perhaps it's a golem spell, using the metal of something in your inventory to create an automaton.
Going back to the skill/object acquirement by wandering... Such a system could be mixed with a clue system. Some measure of control could be sometimes offered to the player by providing them with rumors and other hints of what general direction an interesting object may be found at. Any number of degrees are possible with predictability.
Anyway, I could go on forever (and probably will, in my game sketches), but the point is that I wish RPGs offered less predictable experiences. I wish they did more to invoke my sense of wonder and inspire memories. "The time I accidentally changed myself into a small dog" is more memorable and fun than a particularly rough fight at the such-and-such camp (one of the 50 times I fought there).