cc, my understanding (which there's a high likelihood that it isn't correct) is that the compulsory part had already come into play and those who weren't using them properly were already having listings removed.
i believe that selecting "does not apply" from MPN / UPC etc was going to fulfil the requirements for having product identifiers in listings in those must-have categories.
the only info i can find on ebay australia regarding product identifiers is this page - http://sellercentre.ebay.com.au/product-identifier-landing
it doesn't answer the question about what happens if your item doesn't actually have a product identifier though. there is a question down the bottom which has an answer as to hand-made or one-of-a-kind items, but i think if you want to list them as "new" - you may still be required to add a brand / MPN / UPC etc.
hopefully, it's a case of the "Does Not Apply" still being available - but otherwise, i can't find any other relevant information :]
