This is a linux (and similar) commandline only feature request.

Bash has a default completion, which means it completes every argument as a path name. In order to complete stuff like --parameter or options that are not path-related (e.g. numbers) or to specify files ending on some pattern, one has to write a bash completion script. Once done, you can type

lmm<tab>--s<tab>4<tab>--r<tab> ~/my-p<tab>

to get something like

lmms --samplerate 44100 --render ~/my-project.mmz

As I wrote many of those scripts recently, I'd like to write one for LMMS now. Any concerns before I start?

Also, if I write one, if a project file is expected, should it automatically add project files from the LMMS working directory to the completion list even if you are in another directory? E.g. should lmms --render so<tab> complete to lmms --render <lmms working dir>/projects/song1.mmp automatically? The advantage would be quicker navigation to projects without typing your LMMS working directory path; the disadvantage is that you might add a bloat of files even if you don't want to complete from your LMMS working directory...

Concerning the milestone, this could even be done for 1.2.0, if wanted, as it does not affect the LMMS binary.