Here we have people saying about how King K. Rool has no more chances due to the costume. When the fake Meta Knight picture came up(before Meta Knight was actually confirmed) there were people who were going that Meta Knight was cut and so and so. Now, it's up to you whether you want to call them idiots or what not then, but it's still a case of people overreacting.
Looking at the current DLC costumes, a good majority of them are characters who people practically expected not to be DLC playable:
Mega Man X(in Mega Man's Final Smash)
Dunban(in Shulk's Final Smash)
Proto Man
Isabelle(Assist Trophy)
Mega Man.EXE(in Mega Man's Final Smash)
Zero
Akira
Jacky
Heihachi
K.K. Slider(appears in the Smashville Stage)
Chrom(in Robin's Final Smash)
Now let's look at the ones people want to be playable:
Inkling
King K. Rool
Only 2. And one of them is one that people have thought the possibility of being Post-Ballot DLC(including you, back in the Leaks Group). And yet already we are saying that because those 2 are DLC costumes that it means they are never going to be playable, when all the other costumes are characters people practically expected not to be DLC.
This shows how much we know very little of how much the costumes mean for the character. As You said, we don't know if such costumes affect chances and what not, but here we are practically going over the top about how these costumes mean they can't be playable, despite the fact that the developers have teased us with and made fun of similar issues, both with the Meta Knight costume and Meta Knight and with Koopaling Roy and Fire Emblem Roy. And we ALL know how much the Roy argument was used back then and how much it got invalidated with FE Roy's appearance.
Basically, it's too early to tell if the costumes mean anything. So let's just wait until after the Ballot is over and the Ballot DLC starts coming up.