>Moreover, in Plan-9, many of the "good old things" were removed and a lot of incompatibility was introduced in the system with respect to the other Unixes. This prevented many different companies to even start thinking of porting their applications to Plan-9.

This is fundamentally why plan9 didn't take off. It was too different and not better enough.

Platform technology marketing is being on the right side of a nuanced dichotomy:

1. You need to be different enough to be noticed and given attention 2. And better in the eye of the user (which implies familiar)

For example, OSX was a great success among hacker types for this very reason: It was different yet familiar (Most UNIX-y stuff just worked on OSX thanks to its FreeBSD lineage).

Another example is Go: It's different enough from the previous generation of server-side languages to command attention, but its syntax was very much in the C language tradition (And it articulated its "betterness" well, such as performance gain over Python/Ruby and ease of use over C/C++/Java).

Fundamentally, Plan9 was way too different from the incumbent without any clear advantage.