As for the unfeasibility of the original idea, I believe you but would like more information if possible. Why is it impossible?
On top of potentially overwhemling the game with graphical effects, (Especially in 4 player matches if there's more than one Roy), there's no easy way to say "If character is within x units of a character," without it also triggering on stage hurtboxes, items, etc. and certainly no way to do so on the 500 or so subactions that every character has without putting a line of code in every single subaction. Not to mention having to work around existing effects that may or not be around, working around animations where the sword may be sheathed at one point, etc. On top of likely not looking all that great as a universal effect, it's not really feasible anyways. And with our team's limited resources, we're trying to get the most bang (Cool new features, art, and quality gameplay) for our buck. (Time.)
As with the gameplay comment, people should probably look into the process of modifying Brawl themselves before requesting complicated (or seemingly simple) code to be done. It's a very limiting system that we're stuck in, and honestly amazing that we're even able to do what we can.
I'm not trying to single you out with that bit above, for what it's worth. There's a ton of people that try and make "simple" requests without knowing exactly what it is they're asking. And having to break-down why it's infeasible gets real old after the first few tries. (Also uses up that precious "time" resource.)
Anyways, I'd really recommend giving Roy (And the rest of Project M) a try. Despite his superficial similarities to Marth, he's definitely his own fun, crazy beast. Plus fire.