To understand the UNIX market of the early to mid 80s you do have to realize how many of the soon to be big / big companies were using M68000 and better chips. Porting UNIX, which is as portable an OS as they come, to a new arch like Z80000 or whatever and then getting important applications ported would have been beyond Commodore's capabilities. And for those who've not seen what could be done with mid 80s UNIX, go try NeXTSTEP in virtualbox (the hw is really hard to get, although it's brilliant). That GUI was a generation ahead from what was available at the time!
