When you use rails g scaffold blah blah
it will always produce non-final code, so why not have a scaffolds folder with as many dummy code examples as possible which can then be transplanted into the actual production code.
For example nested forms or select box code or whatever might be specific to a custom generator (mobile or whatever)
This could be very much like "snippets", a scaffold could then make many more assumptions and potentially create non-working code, like assuming that something_id is something that can be used in a selection box and that "name" is the value of an option.