You could, but no normal Unix app will understand it or be able to use it, since this is one of the things that the Unix creators removed from the more complica

You could, but no normal Unix app will understand it or be able to use it, since this is one of the things that the Unix creators removed from the more complicated forerunners of Unix to make their smaller, simpler OS. Sadly, this simplification was, IMHO, a step too far and a bad thing to remove. But Unix's namespace is much simpler, and doesn't really understand and incorporate extensions and things either. Which is a limitation but it makes it much simpler. The fact that most Unix GUIs, from NeXTstep to KDE, put back in and use file extensions to associate files with applications shows that this is in fact important functionality. Without extensions, having version numbering doesn't make as much sense. But a Unix with file extensions and file numbers would be less like Unix than is, say, Plan 9 or Inferno.