Yeah. Any company could become a console manufacturer at ANY time. Sony originally only made software, but in 94 or whenever it was they broke their alliance with Nintendo and came out with the Playstation. The same is true with Microsoft who were also originally software manufacturers, but then they jumped in out of nowhere with the xbox.
So why couldn't Infrogrames/Atari do the same? The Atari brand name still holds some credibility, so if there was a new system named Atari something or other, then people would take notice of it. It doesn't need to be Atari, though. EA could jump in out of nowhere with a console, or Ubisoft, or SEGA once again...
Edit: And as a matter of fact, I think Nintendo released some of their earliest games on the Atari 2600 before they created the NES. So again, what's to stop Atari or EA or someone from deciding they can be like Nintendo and make their own console and use their own games to sell it?