But a "Full" Steem account cost 3 Steem or RC. If Steem hits 5$ it would be 15$. I think it is way to expensive for a really big scale, because there need RC too.

And If a Forum with only 5k Users want to onboard without guest accounts ( Because there want to use there own SMT), it would take forever.

The same with Online Games ( here can Wallet addresses works maybe really well).

The Wallet address Accounts can work, but it isnt tested and finished.