thanks you for confirming this (I already suspected as much).
Well, we have all our regular users in LDAP. We plan to have "normal users" and also "coordinators" that are allowed to invite guests. So, yes, to be able to assign LDAP users to roles is very important to as. It is also probable, that we will have guests in the LDAP too.
I think the requirements for LDAP users are more or less the same as for users coming from shibboleth, so it would also be very nice, if we could implement the feature to store the institution in LDAP.
If I can help in any way, please let me know.