Without the ability to style them, this will not get widespread adoption. I am all for consistency in browser inputs, but unfortunately, that isn't what designers and clients demand. That specific look and feel of the datepicker, with those blue colors, blacks and sharp corners just isn't going to cut it for a lot of people.
I think we will eventually see full styling support for these datepickers. Until then, this is cool, but something I won't be able to use except maybe on a personal project. I know that if I slid this into a project, the first question I would get is, "Can we change the way it looks?" Maybe I just need to find less demanding clients.