I believe much of the team that was working on the S900 left Commodore with Jack Tramiel, and were involved with the design of the Atari ST.
In particular Shiraz Shivji, who was the main designer of the ST, was part of the S900 project.
Pretty sure the S900 was effectively dead before the C128 project was even started.
And in any case the S900 was a monochrome business computer, aimed at the productivity market -- a segment Commodore later targeted with PC compatibles instead.
The C128 was targeted at consumers who wanted to run C64 games.
They had an interesting hack to connect to a high-res monitor. Timing wise they had to stick to the standard TV timing otherwise regular Amiga software would not work. So they created a hack where the Amiga would send 4 screens of pixels that would then assembled and sent to a high-res monitor. Screen refresh rate was very slow though.
I still have a (printed on dead trees!) manual for Coherent 3.2 (286 version, circa 1990-91) kicking around. Ran multiuser (login via tty or virtual terminals on the console) in 640Mb of RAM, off a 10Mb fully installed setup. If I remember correctly you were limited to 64Kb code & 64Kb data per process, though ... (Coherent 4.0 removed the addressing limit).
Wow. That could have been something! Might have been a commercial flop, but it would have exposed a lot of young folks to some useful ideas a decade or two before they otherwise would have been exposed.
Interestingly all 3 of C900, C128 and the Amiga are/were to be ~1985 machines (maybe 86 for the C900). I'd think from the specs (memory, CPU power, multitasking OS, hard drive as standard for the C900 etc) point of view the C900 was competing more with the Amiga than the C64-compatible 128k machine that didn't have architectural prospects of addressign more memory later.
In particular Shiraz Shivji, who was the main designer of the ST, was part of the S900 project.
Pretty sure the S900 was effectively dead before the C128 project was even started.
And in any case the S900 was a monochrome business computer, aimed at the productivity market -- a segment Commodore later targeted with PC compatibles instead.
The C128 was targeted at consumers who wanted to run C64 games.