Domitius:
Would any of the NPCs swap half a bp for services, Rikka for example may want to extend her smithy.
To some extent she already does - but only within the Kingdom rules. For example, when someone build a Sword School, watch tower etc ... Rikka or one of the other smiths makes the weapons / armour etc. Exchange of services is the basis of the BP economy.
However, there is no exchange between BP and adventuring items priced in GP :P