Platinum AU cards may be relatively cheap and cheaper than paying $50/guest visit, depending on the pattern of behavior and what Amex decides to do with AU card fees. [Those cards allow entry too.] Then it's a question of whether the average number of Platinum AU cards on Platinum accounts could possibly increase so much that it makes lounge crowding more likely than if Amex maintained the current guest policy for these Platinum cards. I doubt it, but I also don't think it beyond possible.

I wouldn't be surprised if a materially higher annual membership fee for Platinum card accounts meant that the likelihood increases that a higher proportion of the post-fee-hike remaining Platinum card base would be willing and able to pay $58-200 per Platinum AU card than is currently the case.