I don't think "Roy being a clone" is automatic, especially since "true clones" weren't in Brawl, and semi-clones and characters with a "few borrowed moves" is the norm.
Roy's moves, movement, and sword fighting styles in his game (Fire Emblem 6) are completely different from Marth's (FE1, 3, 11, and 12) and Ike's (FE 9 and 10). Marth is a super quick speed attacker with swift movements and little after lag. Ike has loads of power. quite some lag before and after, and little sprinkles of speed here and there.
If Roy is how he is in Fire Emblem 6 in smash, and is like I imagine him, he would be unique. Roy would noticeable speed. Not great, just good. He would have minimal lag, but not always afterwards. Deceptive power, similar to how my friend SuperSkeetBro describes Ganondorf in Melee as having "deceptive speed." While this is just me defining Roy's characteristics, if you add in that he does a lot of stabs and lunges like in Fire Emblem 6 (which Marth doesn't use), then you could have an interesting character in smash IMHO.
And Krom, could be a clone. I really don't see why having two new additions be wasted on these two possible clones would be a good idea.
Technically most potential newcomers could be clones. Toad, Bowser Jr., Paper Mario, Waluigi, Dixie Kong, Bandana Dee, Krystal, Plusle and Minun, Zoroark, Samurai Goroh, Black Shadow, and Louie are all commonly mentioned potential newcomers that could all easily be/have potential to be clones, semi-clones, etc.
I mean, it wouldn't be awful, but it wouldn't be amazing. TO ME, anyways.
Fair enough. I just thought I'd throw out my vision of Roy based on his Fire Emblem 6 appearance. I think I'd like to also share
this, and
this, and
this.