> What if default sucks for some files and other variant suck for different files (eg pdfs with bunch of text (okular is nice for these) vs pdfs with huge svg (okular is crap for these)) ?
Oh.
Well for Apple they 'solved' this problem originally years ago through their use of resource forks in the file system.
The file manager would read the resource fork for a file and would launch the appropriate application when you opened a file. So while there were defaults for all the file types Mac OS would keep track of the application that created a particular file and things of that nature. That way the system could intuitively deal with applications on a per file basis.
I think Windows has some sort of mechanism for managing per-file stuff, but I don't know what it is.
And, of course, nothing I've noticed in Linux addresses this.