Thinking about it, Ness had no Lucas costume in spite of having his special moves as custom moves, likely due to the DLC being planned. Marth has Roy outfit colors... but those don't change his hair color. So, I guess it's fairly ambiguous (and there's still the small possibility they could just go with his Awakening costume, while both Marth's and Ike's had problems).
Anyway, I really think you're overestimating Lucas' popularity among Smash players. In spite of his unique normal moveset, it was very common to see him considered as just another clone in this forum itself. And he was from a Japan-only game on top of that. The fact that we're getting him at all suggests to me that, for returning veterans, ease to implementation is actually weighting quite a bit as far as these DLC character choices go, which is the main factor that makes me think we might get Roy too.
Roy is the main character of one of the least popular FE game in Japan with a clone moveset minus his b special which is the same minus the added explosion effect casuals get excited for. Had he not been in melee nobody would be giving him any serious consideration.
The only advantage Roy has as a cut vet coming back is that he'd take less effort to make because you could start with Marth as a base and just tweak a few things.
"One of the least popular"? Biding Blade sold more than every FE after it in Japan aside from Awakening. He's less popular among FE fans worldwide, since the games weren't localized until Blazing Sword, but his game at least was fairly popular in Japan.