This regex is the one I used to extract options from man pages, not to parse the command line (which is simply a wrapper around Python's shlex).
Bash autocomplete specifications are messy, but you can sidestep a lot of the mess. You're allowed to run an arbitrary command to generate the completion list. I was envisioning some kind of standard option grammar that the autocomplete program would interpret for a given tool. The grammar would be partly generated automatically, but would likely need hand-tuning.