Yes, that is the biggie; Atari were offered the chance to distribute the NES in America under their name and turned Nintendo down, which has to be biggest no-no since Decca rejected the Beatles. ... This could potentially give Nintendo a virtual global monopoly, at least in the 8-bit era.
From what I've read (as an Atari enthusiast, although I can't cite sources off the top of my head), Atari's negotiations with Nintendo to gain exclusive distribution rights of the Famicom in the US were not so much intended to allow them to actually
distribute the NES, but rather, to bury it in favor of the next-generation Atari console, which turned out to be the 7800.
Then, Atari CEO Ray "the Czar" Kassar was indicted for insider trading, the ET debacle led to the video game crash of 1983, and the next year Atari was sold to Jack Tramiel (formerly of Commodore), who gutted management and had no idea about the negotiations with Nintendo of Japan. Two years later, Tramiel discovered the 7800 prototype in an Atari warehouse and rushed it to market -- by which time, of course, it was obsolete technology. Had the 7800 been introduced in 1983 as originally intended, it likely would have been a market leader.
To me, the best POD would either be all the way back in either 1976 (when Nolan Bushnell sold Atari to Warner Communications in order to raise funds for the mass-production of the 2600) or in 1978 (when Bushnell, amidst mounting tension with Warner's button-down management style, resigned in favor of Kassar). I think there could be several interesting alternative possibilities:
1) Bushnell could have sold Atari to Motorola instead of Warner; this means that the first-generation Atari computers (and second-generation Atari videogame console like the 5200) likely run off of the MC6809 instead of the MOS6502.
That also gives you a potential second-generation Atari computer (1200XL equivalent) / third-generation Atari videogame console (7800 equivalent) based off of the 16-bit MC68000 as early as 1980/1981. By 1984, Atari might still buy the 8-bit Famicom and market it as a low-end, younger-market alternative to its high-end videogame consoles -- kind of the role that Nintendo has today, now that I think about it.
2) Atari remains a Warner property, but Warner agrees to sell the (then-unnamed) Atari Computer Division to Joe Keenan (of Kee Games, essentially a Bushnell proxy) in 1978, eliminating the tension between Bushnell and Warner and allowing Bushnell to remain as CEO of Atari.
Under this scenario, Atari would focus all of its efforts on developing and marketing the 2600 and future videogame consoles, while Kee Games (maybe doing business as Syzygy?) develops the "Colleen" computer (the would-be Atari 800). Possibly Bushnell and Keenan sell "Colleen" to Apple; after all, Nolan Bushnell once hired Steve Jobs way back in 1976. "Colleen" gets named the Apple III (or perhaps the Apple IIgs) and, along with its successors, is the biggest-selling home computer line of the 1980s.