I think this thread may be a candidate for merging with Feature Request: Retention by Destination Usage
I think this is my #1 feature request for VEB. On endpoints, I've been using Windows Backup. It fills up the disk and then starts culling old restore points as needed to continue on forever. VEB requires setting the exact number of restore points to keep. That means that either I underestimate, and waste space on the destination disk, or have a future backup fail due to lack of available disk space. It would be so much more convenient if I could configure VEB with two numbers for restore points: Min and Max. If the disk fills up, old restore points would be removed to accommodate. If the disk was full at the Min level, then it would fail.
I think this makes a lot of sense for endpoints with dedicated backup storage, but not so much when backing up to a VBR repository or SMB folder. So, I can see what the current design is based on. When the storage is not dedicated to a single system, you want a rigid retention setting. But VEB is great for home users and other systems that do have dedicated backup storage.