This is an optional part of the thumbor release. It would have to be applied only to places where the new varnish 4 + thumbor stack is used.
The Thumbor release doesn't depend on this. We could do it now, even, we'd just have to tweak the thumbnail url scheme slightly through the whole stack.
Regarding T19577, timestamp-based versioning tends to be fragile in my experience. Particularly in a clustered environment where separate DCs could race on generating the same thing.