A private journaling application can be done in the dataform. What remains is restricting access to certain users. Currently you need to create groups and grouping for the designated users. But this should probably better handled by module restrict access settings (after all, grouping is essentially an access setting in the course level). If hacking I would hack the latter.
General help
Auto-create groups by last name, first name possible?
Müzakirə kilidlənib, beləliklə ona cavab vermək artıq mümkün deyil.