There are many problems with this suggestion, but the main one is that it would transform the PB from something that is "available" to an entitlement.
If you'll give me a voucher I would be expecting to be able to use it in meaningful places and with adequate quantities. This would have to transform the PB from a marketing ploy which now allows IHG to sell as a plus of the program and dump empty inventory, to something that has to be meaningful and plentiful.