Don’t know if this is even technically possible, but it would be nice when syncing from a desktop to know the free space on the device (or cloud) that you are attempting to sync to, and a warning if the sync will exceed that limit.
I would add some sort of progress status as to the upload process. I can’t tell if my video has a problem or not.
It should also have some sort of failure message if the upload times out.
Early 2021 clean-up: implemented (Plex gives a warning if files cannot be synced due to capacity issues; option to set limits to sync capacity)