Continuing with assignment... I've detected that all the assignment types use the "submission" file-area for submitted work (upload & upload single). But the online one is using one different file-area: "online_submission"
So we need this difference? If so, then all the assignment types should have its own area. Else all them should share the "submission" area.
This is not really critical... but we should decide about that and apply the decision to all the types.
Note I've seen some harcoded "submission" uses within core assignment/lib.php, so perhaps it would be better (easier) for now to use the "submission" file-areas for all the core assignment-types. Later, we can move if decide the split is the final situation.
PS: Any change requires both change in the code and change of existing files to the final target filearea.