I haven't taken too deep a look into the Vim syntax engine yet. So I don't know how hard it is to do more complicated alterations like changing indenting and code folding. However for doing simple keyword highlighting it seems pretty straight forward. I've created a repository vim.fortran
that I'm planning on building the Vim syntax package in. At the moment it contains a single file that I have in my local .vim folder containing a handful of simple fixes. If you want a larger example you can find the full fortran.vim file in your Vim install folder. I don't understand all of it but you can figure out a good deal by just hacking around in it. I'm planning on putting in some serious time on this after the weekend.