That's true, but the reasoning that Draco becomes chosen is as a punishment essentially, against his family. Because of Lucius failing to retrieve the prophecy from Harry and all that good stuff in the Department of Mysteries, the Dark Lord chooses him, and he has to do it or his family will die. Another reason that Snape ends up having to kill Dumbledore is not just because of the curse that was on the Horcrux Ring and the fact that the Headmaster asks him, he is also makes a bond with Narcissa to protect Draco and to fulfill his duty for him if her son can't do it.

That being said, I'm sure we can think of a way to switch it to Ron. Like perhaps they pick him, because he's willing and also has been much closer to Harry than Draco, which in turn means he's closer to Dumbledore. However, when it starts to get worse, and Ron is beginning to feel the stress and pain of being a Death Eater, I think he'll start to maybe realise that his decisions were in poor, bitter taste, and that he has made his family a prisoner in serving Voldemort. So this will make things a lot worse, and yet, it will be a paving stone for him to get back on the right track.

And yes, I feel pretty psyched up for this RP~ It's going to be interesting to see characters develop so I'm looking forward to that, as well as the aforementioned grit-and-fluff.