That's pretty much true of any django release... you can stay on it if you so choose to. It will get security updates/bug fixes for a bit and then they will stop coming. You're free to stay where you are if you want.
It turns out that most developers have a desire to move to the next version if it's not too hard. There's still COBOL programmers out there too and that's perfectly fine.
Django has made the process as smooth as it can be. You can upgrade to python3 while maintaining your Django version. Then update to the next Django version as a separate step. It's fine to have waited until now. You can keep waiting if you want but it's getting to the point where you should really just do it. It's not so bad.
We switched and python2 --> python3 was bumpier and more work than most Django updates we've done (we've done pretty much every one since 1.0) but it was still entirely reasonable. We're much happier now.
My feeling is that you want to be using dependencies that are actively being maintained. These probably already support py3 - or there's a newer / maintained alternative available.
What's annoying is discovering that it's a struggle to upgrade to a newer OS because you're using some old python dependency that has some C component linking to some library that you're going to spend a week getting working (and then have to continue to maintain).
It sounds like you might not have too much trouble upgrading anyway. The strings and missing libs are the places most people get caught out and it sounds like you're already handling the worst of those.
If I were you, I'd try switching to python3 and see what breaks. When I did it, it took about a day to get up and running again on a reasonably complex project (numpy, scipy etc). One of the main things I ran into was places where python3 had swapped lists to generators etc (eg, some_dict.keys()[0] no longer works).
