We are still doing massive development, once our codebase is stable enough we will move them into small gems, right now it's just a bit of hassle running bundle update for every small increment.
You can plan this migration ahead of time by moving your models into gems stored in, say, vendor/future_gems/. Then just reference each gem in bundler as:
gem "my_models", path: "vendor/future_gems/my_models/"
Once you are able to break them out completely, just remove the path reference and use a gem server instead.