Nicolas,
No, it's not. I started it, but then got sidetracked to other things (school) on the way to writing a PayPal payment gateway (that was the original motivation).
My changes only require modifications in some of the e-commerce checkout files, plus a couple extra procs on e-commerce and a couple extra "methods" on the payment gateway service contract.
I'll coordinate with Bart (the e-commerce maintainer) about getting those changes in to e-commerce.
-Roberto