One feature that I appreciated a lot with CrashPlan (when they still had a personal plan) was the ability to have an infinite (or independent) retention period for the last version of a deleted file.
The idea would be that when a file gets locally deleted, the last version in the back-ups is kept forever/for a configurable time.
Currently, with restic, if I’m not mistaken, deleted files might be pruned out off all snapshots if the file only lived for a short amount of time. Also, there is no way to ensure that the final version of a file is kept when removing the snapshot containing this final file (just before it was deleted, i.e. the following snapshot would not contain the file).
One idea could be to check, when removing snapshots, for all files whether the following snapshot still contains that file. All files that are not contained by the following snapshot could be added to a “fake” snapshot which would effectively replace the removed snapshot and only reference all the files deleted between this snapshot and the next (multiple directly adjacent fake snapshots could be merged into one).
I hope this makes any sense