I think the BRG form should retain its old form for 1 possible exception:
When spg.com is sold out completely sold out (not just a particular room category), but a 3rd party website is still selling rooms for the hotel.
If we are required to have a confirmed reservation in order to file such a BRG, then this BRG cannot be filed at all (under the new rules) as there is no way to have any reservation on spg.com since it is completely sold out, and we cannot file BRG based on availability for 3rd party websites (and none for spg.com).