The possibility to choose individual Rem or a certain number of Rems to backup, instead of having to backup all the rems once
Are you referring to Backups created by the Export option? This is already possible.
Zoom into a Rem at the desired hierarchy level by clicking it’s bullet point or group same hierarchy level Rems under a Header, create Search Portals, etc. then:
→ Open the Document Menu ( the ... icon in the top right) → Export.
Was this what you were looking for? 