That's not how it works. There's no need for melee unless Smash 4 is a complete and total bust. There's going to be a lot of overlapping between players for both games and Smash 4 would draw more new blood.
Not true. Apex 2015 shows there's very little overlap between the two and people like Mang0, PPMD, and etc. definitely would not compete in Smash 4 at EVO. All the main big sponsored players for Melee aren't interested in Smash 4. It draws a completely unique crowd of players and it has more entrants than Smash 4 at Apex 2015 -- if there hadn't been a 1024 cap it would have gotten close to 1,200 entrants easily.