I don't think that idea could work. A world composed entirely of magicians is just a tad too farfetched...even for fantasy. You'd have to write some major barriers into the magic system or the world simply could not survive. They'd tear each other apart in lust of more power. I reckon if someone managaed to complete a novel like this, it would flop. But hey, that's just me.
Yeah, it would be certainly *difficult* to conceptualize, let alone write. But there are some elements in literature (usually more of the science fiction variety I think) that had societies where all the members had certain powers. After all, to pretty much every other type of creature on our planet, the ability to use tools is pretty exceptional. The introduction of opposable thumbs gave us a huge advantage over all the other creatures of the planet (and beating the other apes to the punch). Imagine a world where us plain old humans were beaten to the metaphysical punch by some other type of being.
I would imagine a post-scarcity world would spend a great deal of its time trying to push the boundaries of their physical constraints more than anything. When you stop having to worry about procuring food, shelter, material goods, or even energy sources, what would creatures pursue? I imagine, for us, we'd definitely push outward into space and exploration, which is why this concept is probably closer to the domain of sci-fi than fantasy, though it would certainly contain elements of both. And regardless of the availability of your every want, time is still a (relatively) scarce resource.
There are plenty of approaches that could be pushed, but it'd definitely require a certain conceptual and literary finesse.