Hi. Thanks for replying. I don't disagree with anything you said, but I still think this would be good at least as a commented-out-by-default bit of config.
In my day-to-day use of the machine I routinely use /var/cache/apt/archives to, for instance, access the previouly-installed packages; older versions perhaps. This cache is always there, and I don't manage it. 99% of the time the packages I want are there. Extending this idea to schroots doesn't seem unreasonable, even if there are corner cases that would make it not perfectly-nice in 100% of cases. If I propose a patch to add this as a commented-out-by-default option in the config, with your concerns placed in a comment, would yall accept it? Thanks