I have found no change or break in functionality
I could not login and there is no mention that you have to use your email now anywhere. Fail. Next tried to recover my password, the recoverylink on the TS website leads to a MW-account-only recovery option. Fail. I found out about the changed login via google, and only because i found a forum posts here that complained about this exact thing.
questions about the longevity of the service without a viable economic model
If you want to build a viable business with managable risk you have to get pricing feedback from your customers from day one and not after you got a metric ton of users that are used to freemium.