Courtesy of Gamasutra's interview with Takeshita San:
GS: Essentially, this game isn’t actually a Famicom game. If it were burned to a cartridge, it wouldn’t actually run on a Famicom. It is a duplication of the Famicom capabilities, but within a modern game engine and technology.
HT: Well, when you put it that way… (laughter) This couldn’t fit on a Famicom cartridge. It’s too big. It’s too much for that. It’s really emulating the old style of games. But we’re hoping that when people play, they feel the same nostalgia that they have when they play the original games.
GS: You talked about how people were trying to graphically exceed the capabilities of the Famicom, but what about the temptation to exceed some other capabilities, such as flicker, slowdown, sprite limits, and stuff like that? Was it really hard to get people to stay within the confines of what they could have done, if this had come out after Mega Man 6 in 1993?
HT: Yeah, there were some things, like you couldn’t have more than three enemies on the screen at once, so we had to make sure that that’s how it stayed in our game. In the part with the dragon with the flame, [there should be] flickering, and whatnot.
In the options of this game, you can adjust that, unlike the old games. We purposely put some of those old-school bugs into this game, so it does recreate that feel.