I'm synchronising entire large folder trees to stack as a cloud backup, but I'd like very much to be able to exclude some sub folders from sync. The amount of exclusions is very small compared to the amount of inclusions, so to select every sub folder in an inclusive way is not feasible. I'm using the windows sync software. I believe best usability scenario for my wish could be via integrating a command into the file explorer context menu (aka right click) to allow exclusion of files and folders from sync. And, if this is already being implemented, it's probably a low hanging fruit to allow to also include folders to sync in this way as an alternative to directly specifying it in the sync software UI. Alternative, simpler implementation could be of course to set up exclusion paths via the UI.
Remark: Currently there is a checkbox next to every sub folder in the UI, but unchecking it prompts the message "Unchecked folders will be removed from your local file system..." and this is of course the opposite exclusion direction (could --> local) from the functionality I suggest (local --> cloud).