It's possible, but I'm not sure how robust it will be. There are a lot of heuristics being used to guess what the options are, if they expect an argument, etc. So when feeding it with a command that was typed by someone, which is most likely correct, it's fairly easy to look up each option in all the possibilities. Not to mention some commands have a very complicated set of rules (e.g. find), and the position of some options is context sensitive, which explainshell isn't (it could be, but that would require a lot of manual work).
It's interesting because I had an idea once to do the opposite: see if explainshell could use completion files from bash/zsh/fish as another source of options besides the man page.
Completion scripts from bash are far too much of a kludge to extract information from.
Most tools are written in C, and the standard way to parse options in C is with getopt(3) or getopt_long(3). I actually looked into searching the compiled binary for the getopt_long structure, but that wasn't so easy. Since these functions have information on all the possible options, it would be nice if there was a standard way to get them to spit out the option list.*
See my reply to your comment in another thread. It would be a killer app to have better autocomplete support, but I can't offer assurance that it's feasible.
* I had another idea: you could use ELF tricks (LD_PRELOAD) to load a different version of getopt/getopt_long that would spit out the specifications.
Fish shell does something like this. It's nice to start from, but there are definitely not enough on their own. Git for instance needs extra rules to complete branches and so forth.
