This is tricky because store information is based on hash ranges, so this will not work if the 2 flists uses different stores because rfs will not know which store to use if a blob hash matches 2 stores.
rfs will try all stores that matches but it also means there can be a performance hit for each blob it has to retrieve.
The merge must respect order of merge (like overlay) which flist is laid on top another flist
The files from top flist should hide the ones from lower level.
The dir from top flists should "merge" recursively with lower dirs
This is tricky because store information is based on hash ranges, so this will not work if the 2 flists uses different stores because rfs will not know which store to use if a blob hash matches 2 stores.
rfs will try all stores that matches but it also means there can be a performance hit for each blob it has to retrieve.