Okay, but you still need a Steam ID in order to play a game of TF2. Which means account. So maybe you have to have spent at least $9.99 on a Steam account to play TF2, and any other F2P games that opt into this new system. The main flaw I can think of off the top of my head, besides a rise in stolen CC usage, would be money laundering games where they buy a friendly game to qualify, and the net profits get channeled back to them. That's already a problem on Steam, and money is more traceable.
But, you know, do something, right? Make it harder. They can't just throw up their arms and give up. Hopefully they're not doing so. This is going to continue being a problem in other and future titles.