Actually, I'd argue that most of the newcomers we got in Smash 4 weren't heavily requested at all.
- Wii Fit Trainer was completely Sakurai's handiwork.
- Greninja wasn't specifically requested by fans, and it got in Smash mainly because of upcoming relevancy.
- Pac-Man was anything but popular, and most people didn't give him the time of day until Gematsu.
- None of the FE characters except Chrom were frequently requested among Smash fans.
- Shulk might have had a small following in Japan, but he was so obscure in the West, Nintendo didn't even bother revealing him worldwide; instead, they revealed him in a Japan-exclusive Direct.
- Dark Pit is Dark Pit.
- Duck Hunt was never one of the retro characters frequently brought up in discussion.
Sakurai does listen to his fans, and that's probably why Villager and Mega Man were two of the first newcomers revealed for Smash 4. However, it's hard to argue that almost all of his character decisions revolve around what the fans want. He adds his own little touch to the roster more than a few times with each Smash game, and I expect this game to be no different.
I don't think you got what I posted. The characters I listed were those that were unpopular or virtually unknown but got in anyways.
-Marth was heavily requested in the Japanese poll following Smash 64 and, being here and on other sites during the Brawl and SSB4 speculation days, I know Ike, Lucina, and Robin were regularly requested too. In the case of Smash 4, most people just figured it would wind up being Chrom and Lucina, not Robin and Lucina.
-Shulk wasn't well known among casual fans but, like the FE reps, were regularly requested by people on sites like here, Game FAQs, Allisbrawl, Miiverse, etc.
-Pac-Man was more of a casual pick but, again, regularly brought up if you knew where to look.
-Greninja is kind of an exception every Smash game so far has had a rep from the latest gen upon release. New Pokemon are about as +1 as you can get for Smash but, seeing how X and Y didn't come out until October 2013, nobody could really put their finger on who they would go with.