The current state of default scopes now is broken (for me). I have tried using them many times but they always end up being more trouble then they are worth.
One of the biggest shortcomings I’ve had is the inability to remove just the default scope from the relation as sreid mentioned.
Unscoped does what it says. It removes all scopes from the relation. It would be nice to have another method that only nullified default scope. Something like ‘custom_scope’. Not sure if that’s quite the same intent as th OP, but if included it would be cause enough for me to try default scopes again.