Of course, plan versioning is introduced in a later version, and Rafts (which allow for Git-based storage) is coming in 6.2.
I definitely understand the hesitance to upgrade, but worth noting ---- for once 6.2 comes around we'll offer some great migration tactics to let you pull applications from really old versions of BuildMaster. We'll also better support multi-instances of BuildMaster, so each group can upgrade as they'd like.
That said, the Plans database table will contain your OtterScript plans. Not sure if that's a good solution, but pulling from that table will give you latest versions.