Any NTFS drive has a X:\System Volume Information\ and a X:$RECYCLE.BIN\ directory that
should not be backed up.
Duplicati should exclude this directories automatically if it recognizes a
whole drive X:\ being specified as a backup source.
You can use the special {SystemFiles} exclude filter to exclude System Volume Information and several others. I thought $RECYCLE.BIN would be there, but strangely it is in the special {TemporaryFiles} filter.
You can find some of this documented here.
I agree that the two items you mentioned, as well as things like pagefile.sys, hiberfil.sys, etc., should never be backed up by Duplicati and should not require the user to explicitly exclude them.
The system files filter for Windows excludes the RECYCLER folder. Does this contain the recycle bin contents as well?
Just checked a bunch of Windows VMs I have:
Windows XP and older calls it X:\RECYCLER
Windows Vista and newer calls it X:\$Recycle.Bin
These are all on NTFS drives. Interesting about FAT drives using a different name. I might do some testing with the various Windows versions to confirm.
For consistency I think both should be in the same special exclude set.
Also, it might be better to switch to using API calls to determine these folder names instead of hard coding paths. Seems most (but not all) are hard-coded.
FAT Recycle Bins
NT4 - X:\RECYCLED
2000 - X:\Recycled
XP - X:\Recycled
Vista - X:\$RECYCLE.BIN
7 - X:\$RECYCLE.BIN
8.1 - X:\$RECYCLE.BIN
10 - X:\$RECYCLE.BIN