Yes I did, thanks, I've also checked out: https://reactstrap.github.io They're both building on top of the v4 alpha, which feels like a sinking ship indeed. Though it could all change ofcourse, they are also updating the official themes to v4 so maybe we'll see an official release this year after all. But then again, it might be too late ready...

Why does Bootstrap 4 feel like a sinking ship?

Because v4 has been in alpha since august 2015, and v3 hasn't had significant updates since 2015 either.

Over the years I've gotten an incredible amount of value out of bootstrap and 3 has been great but the uncertainty over 4 and the huge delay has made me start seriously looking at alternatives over the last few months.

Semantic and Foundation are both on my list of things to look at.