The blog post links to a tweet and that tweet has a couple more details. The new keras is going be tensorflow-only and build on top of tf.contrib.layers (so a complete rewrite).
Theano support will continue for as long as Keras exists. This integration changes nothing for existing Keras users, only for TF users. - https://twitter.com/fchollet/status/821090410659344384
Rather than a "new" Keras it sounds (I could be wrong) as if the Keras API will be included now with TF as an alternative way of interacting with TF (as it has been for some time) and simple bundled with TF.
Theano support will continue for as long as Keras exists. This integration changes nothing for existing Keras users, only for TF users.
https://mobile.twitter.com/fchollet/status/82109041065934438...