Reasons to Upgrade
Samsung is going to have to create a number of compelling features in order for users to upgrade their phones from for instance, a Note 4 to a Galaxy S7. Samsung's user base is based upon expandability (storage), control (removable battery) and diversity (S, A and J series). Hence, it is interesting that Samsung decided to take away a few of these features that might be considered core to the user.
I feel that Samsung's user base is also one of the biggest supporters of the Phonebloks -- it is interesting that Samsung has not experimented with a semi-modular design as well.