You can do that already if you like (combined rolling snap and delta backup). But what's the point?
Oh, wow. You can combine backup methods in the same job (as long as they are compatible methods (i.e. Delta and CR). This is cool. I currently have separate jobs for my deltas and CRs. I'll need to make time to make the changes, but this will simply things greatly. I'll even throw in a few extra snapshots to retain. So, yea, this is pretty much what I was thinking of. I didn't realize it was there.
Why would I need this? Well, when my WSUS installed the Xen drivers on all my Windows VMs, I went a day before realizing what happened. A snapshot would have been sufficient, if I had one from the day before. Instead, I restored the backup which broke the chain.
edit: about your previous question, restoring without breaking the chain. That might be possible. In theory, after restore, we should take a snapshot before booting the backup and then re-link the restored VM to the backup folders. It's doable (renaming some folders correctly) but I'm not sure this will be very useful.
I'll look into this when I get some time. Thanks.