It's more work than it appears. And it's work that doesn't seem to have immediate benefit, since Python 2 is still around. Augie Fackler has started tackling it, but even if we do get the change to Python 3 itself, it also requires a substantial rewrite of the hg codebase, since we use strings everywhere. And again, it's a lot of work with no huge payoff.
I completely believe that, and good point about Python 2. I wasn't considering that side of things.
Is it a complicated rewrite, or just big? Superficially it seems pretty mechanical, `bytes.format` to `bytes_format` (though finding them might be hard). I never feel like I have free time, but I don't tend to get exhausted from things like that, maybe I can contribute a bit. It would be good to get exposed to some decent, real Python code :)
