hmm, I see what you mean... and remember that many spool at the factory of mendel-parts seems to work like that. The coil is put in a plate with a hole in the middle and hanged just over the machine.

Maybe we think of unrolling it because some filament are sold on a spool (like the ultimachine or makebot) that function like that, and even with just the coil of filament I found it easier to unroll than when feeding the machine by pulling the filament (the twist caused also a little mess *DONT_K
NOW*).
But it would be interesting to see this other approach for a spool :)

I see most people try to have their spool of material on a spindle, and to have the spool unroll. When unspooling other materials (wires for electrical wiring, yarn for knitting, for example), the end piece that is pulled is taken from the inside of the spool, and pulled straight up (there generally is a pivot point above the spool, on the axis). The spool is then motionless, and the effort required to pull is really small (compared to setting in motion the spool).

The only "inconvenient" (which is not one in certain applications) is that a twist is then imparted to the unrolling material. How much of a problem would that twist be? Does anyone use this technique to feed the filament to a 3D printer?