Hi, @andyfd, my best guess is that will never be supported as it runs contrary to a key design decision in how Netlify site are structured. All deploys are atomic, immutable, and persistent. This means you can publish any deploy at any time as the production version and roll back to a previous deploy at any time.
Being able to delete deploys would invalidate that design.
I would be happy to enter a feature request asking for temporary deploy URLs but, at least for the time being, I think the chances of us re-engineering how our deploys work to support that would be very low.
We would certainly track interest in the feature request but (because it would mean completely throwing out how Netlify works now) making this change would be a massive amount of work and is unlikely to happen unless there was overwhelming interest (which there doesn’t seem to be at this time).
I’m not saying it is a bad idea, only that it is contrary to how Netlify works currently and would require non-trivial changes to implement.