This is the same as the positional argument, and can be passed more than once.
I'm curious what other reviewers think from an API design- the good/bad/skip is a bool, so it feels strange to get the first revspec free, but then need an option for subsequent ones. Can't multiple revspecs be passed in the way a list of files can be passed into file based commands?
The addition of --rev is more to mirror other command that take revset as unnamed argument (eg export). I am totally fine with also making multiple revs accepted by this command.
I fear that this will increase the likelihood that the user runs hg bisect -r abc123, so could you insert a patch before this one to make sure that that is an error?
nit: while you're touching this code, could you also rename this variable to revs to make it clear that it's a collection?