> piracy
Under the original copyright terms, or really any "reasonable to the man on the street" copyright terms, NES games would have been in the public domain long ago. You'd be able to distribute the ROMs freely.
> perfect additional business for nintendo
Nintendo are creating a "classic games" subscription service for the Switch, and indeed, one of the features of these games is that they've been rewritten to support online multiplayer.
But there's a reason Nintendo are doing this (rewriting the games to support multiplayer), and a reason Nintendo released the NES Classic (a bundle product): it's because the IP by itself wasn't selling any more. On the Wii U and 3DS, these classic games were available via the Virtual Console service. But, AFAIK, most of such published VC games were negative-ROI after the re-QAing and marketing costs were taken into account. People just weren't buying standalone NES titles.
And yes, this might be "because of piracy", but only in the most vague and abstract sense. Many people knew that they could play whatever old NES game they wanted on a computer. Many others, though, just still owned a NES and the requisite games; or owned any of those games' later ports on newer consoles. The IP—in its precise form—was "played out."
People who own Star Wars on LaserDisc don't need to buy Star Wars on VHS: there isn't any improvement, it's just another release of the same material. But—like the NES Classic—a Star Wars boxed set of VHSes might be interesting. And—like the Switch's new subscription classic-games service—a Star Wars Blu-Ray remaster would be an improvement. One is a new product that is different in kind; and the other is, actually, entirely new IP, derived from the old IP.
Do note that—assuming the old IP had entered the public domain—this service, which uses the old IP together with modified virtual "hardware" to create an online multiplayer effect, would be perfectly above-board, even though it competes with Nintendo's new derived IP. It isn't itself a pirate copy of the new derived IP, so it's fine.
> whether the biggest icons in the popular culture should become public domain
Actually, "icons" (trademarks) don't have limited terms at all; they're perpetual. But once a work is no longer under copyright, you can then distribute that work all you like, even if it contains trademarked characters. You can't make new or derivative works that feature said character (or logo, or any other kind of trademark) in such a way that it might be misconstrued that the work was created by the trademark owner, but that's it. You can use the original work however you like. Everyone knows who made it, and you're not creating confusion by distributing it yourself, because it's not a modified version. You're just doing the same thing a store does, giving people a copy of the thing someone else made.
This is why satirical caricatures of trademarked characters are fine: nobody is going to think political-cartoon-Mario was created by Nintendo. But this is also why e.g. the movie Wreck-It Ralph still had to license the trademarked characters it used: they're using them as-is, in a way where the brand cachet of the characters makes the movie money.