First thing to mention: Receiving 9 string from a spinning wheel would be a big problem. As I learned from Skyblock, four string make one wool. So if I place 1 wool, I get back 9 string, meaning I double what I put in. Infinite string and wool, to put it simply.
Apart from that, I actually fully support this idea. It allows space for even more transportation items like horse-drawn carriages, which could allow you to have a safe travel, and even have a carriage for one of your friends to ride in!
Circles don't exist in minecraft, and shouldn't :P0 But what I would find comical if the wheel was put into the game, was if they designed it as a sqaure shape, but still functioned normally as a wheel.
I don't like the redstone idea, but I luurve the spinning wheel idea and the wheelbarrow
100% Support. If I did want to make a vertical mineshaft where I could haul my stuff up to the surface, as of now, rail and minecart are quite too expensive for me, so a wheelbarrow might be of good use."Are you nuts?! The wheelbarrow will obsolete the minecart [with chest], since the wheelbarrow will not need tracks!" This just adds 3 kinds of disadvantages to the wheelbarrow to balance it with the minecart. First, you have to pay more hunger than usual, especially when sprinting, which will cost you almost as much hunger as sprint jumping. Second, you cannot jump with the wheelbarrow in control, so if you have to go up a slope, you will need stairs, and you'll need the crafting table indirectly for this just for any kind of stair. (Plus, this adds even more hunger drain, especially when it's a slope going up 45 degrees.) Third, you can't control more than one wheelbarrow (which is self-explanatory), so having chest minecarts set to go to storage, another base, or a build site for a large building is more suitable for mass transport of items in later game. One other thing, I think "cars" will be suitable in Minecraft (99% support), but should be renamed to "Powered Cart" and they will have several advantages and disadvantages over the minecart and horses, Mojango.
Faster than a horse, which can speed up your trip to your nearest stronghold.
Does not require tracks, like the minecarts do, creating immediate savings on iron if you get used to it (or at least finally.)
Allows for the possibility of "Go-kart racing" in Vanilla Minecraft, if you can build you track so there's at least little risk of your "Go-karts" breaking from a crash.
Almost as tedious to control as the boat, and can skid, especially on ice.
Will crash if it hits a non-rubbery block at high speed, and even it colliding with rubbery blocks, such as the new 1.8 slime block and soul sand, will still cost it some durability.
When it does crash, it explodes, and will damage the player, having around a 75% chance of killing an unarmored, full-health (without health boost/absorption) player in one shot.
Does not have a storage space, like the donkey with chest and the Minecart with Chest does, So it's not the best for item transport, you may be better off with a donkey or if mass transport of such, Minecarts with chests
That is all for now, I may add more Pros/Cons to this sometime. Goodbye.