I think marketing is also a problem here. Even frameworks that realize shortcomings of two-way bindings feel compelled to support them because it's hard to educate newcomers to abandon their old ways.

“Two” looks better than “one” on a feature checklist.

Quoting Sebastian Markbåge from React, “Angular is intuitively better to most engineers based on previous experience and ideals. React is better in practice. This is a biased opinion, but based one large org's experience of trying both models extensively.”

Two-way data binding is not inherently a bad idea. In fact, it's awesome in many cases, especially forms and form-like elements.

The problem is that people have a habit of misusing them and start using two-way bindings where they should be using events or similar patterns.

If I remember correctly, the Ember team isn't planning on abandoning two-way bindings. They simply want to give the developer control on when to use two-way bindings and they are going to make one-way bindings the default. That way you can decide if you need live updates or if data-flow control is better.