From a BB post:
" Most of the "The Settlers Online" websites use Ubisoft accounts (formerly known as Uplay) for a very long time already. And now, step by step, we are introducing Ubisoft accounts on all "The Settlers Online" instances, as well as updating the existing implementation to the most recent version. In this thread, you can find answers to some questions that you might have. "
Does this mean we all have to use a Ubisoft account soon?
And yes, what will happen to our existing account? Me e.g. plays from Steam.