You said - I argue that BoQ are not narrative and don't often given detail to specific areas of a build, often just elements, sometimes in a high degree of detail but often just quantities of materials for substructure, superstructure etc. - in short it is not as simple as addinng tasks, durations and dependencies between line items on a bill.

• Agree hundred percent to the point I do not believe a happy medium is feasible. Just use cost codes and reporting from your software.
• At home using the schedule as a billing tool is rare.  We find it easier to enter data, make the calculations and communicate if using Excel only as our billing tool. We consider schedule as a supporting tool but not a substitute to well established billing procedures. 
• We almost never pay advance money for services not yet rendered but payment for materials on site is common at home, this can complicate billings if the schedule is used as the main billing tool. 
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• Please be reminded of potential issues when unpaid remnants of activities in progress (paid to 97% and holding) can distort the schedule by increasing “out-ofsequence” reporting. The following reference gives you how to deal with this.
• The Great Divorce: Cost Loaded Schedule Updating
• Similar adjustments might be needed for Advance Payments as well as for Materials on Site.
• Progress Payment Curves usually refer to value of work in place, advanced payments as well as material on site are not included.
• For those using Primavera P6 the following link might help.

• https://www.slideshare.net/MuhammadMujahid4/loading-cost-in-primavera-schedule-using-resources-and-expenses-r01-80248282

• Financial Periods can be an issue with Primavera P6 and other software.  Spider Project does not have such issues, no need to use different databases when schedules use different financial periods for reporting. 
• I use Spider Project, the following illustrates a way to use the schedule as a billing tool.

You also said - I am using Powerproject - is there a way of switching between a narrative layout that would be used by site manager, client etc and the BofQ format craved by my QS by use of filter?

• Modeling of quantities and unit prices for hundreds of billing items can be difficult, error prone or excesively time consuming if using the scheduling software.
• We rather use Excel to communicate our billings to field people, subcontractors, inspectors, architect etc. Then we transfer the data to our scheduling software.

Good Luck