My 60-character roster with DLC may seem excessive, but consider this:
If all veterans return barring Snake, Ivysaur, and Squirtle, and two more newcomers are in, that makes makes 48 planned fighters. Then add Lucina, the last-minute clone, and Miis as a collective, and you get 50.
That perfect, coveted 50.
Now, even more fan favorites can be included over time as DLC.
I decided on 9 DLC Newcomers + Snake.
Now, that brings us to 60 characters, which is a lot. But I don't think it's too far fetched. Marvel vs. Capcom 3, a comparable cross-over fighting game, had planned 12 DLC characters (however, due to a disaster hitting at around the same time, they were all put in the revamp UMvC3).
Most fighting games now have 5-8 DLC characters included.
So it's not implausible for Smash to get ten DLC characters considering it's large library of unique characters.