The Atari 3200 was a canceled project that would have produced a compatible successor to the 2600. Little seems to be known about it; about the best reference I have been able to find is https://forums.atariage.com/topic/77312-the-atari-3200-system-x/
And then came Project Sylvia, also known as Super-Stella and the Atari 3200. It retained compatibility with the 2600 while offering new possibilities through enhanced sound, graphics and an improved 10-bit processor. It also looked a lot like sandwich toaster, but that's not what killed it. When game designers were presented with the new machine to begin experimental development they found it was simply too difficult to program -- and remember, these people were accustomed to 2600 development which as good as required them to program the TV's electron beam directly!
An intriguing summary; as OP observes, just what could the machine have required of programmers, to look difficult compared to the 2600?
But the particularly puzzling thing is the mention of a 10-bit processor.
Mind you, I do think there would have been merit in expanding the byte to 10 bits. That would have led to 20-bit systems, that could address a megabyte of memory while being significantly cheaper than a 32-bit machine.
But that seems very unlikely to be what is meant here. A backward-compatible game console is not going to get to change anything that fundamental.
So just what did the reference to a 10-bit processor mean?