@sja, you are correct, account will be moved onto an older "underlying technology" and new one lacks some options that the older technology has. New technology has some additional feature such as snapshots. Please click on the following link to know more about snapshots: https://www.idrive.com/snapshots
Once the account has been migrated to old technology, we will not be able to migrate it back to the newer technology. Currently we do not migrate account with data and the data has to be backed up again. However, you can make use of the IDrive Express Service. Please click on the following link to know more about IDrive Express: https://www.idrive.com/idrive-express