Keeping up with the LLVM internal API is really a pain with the six month cycle. Is there a plan to stabilize it in the near future? I can see some open source project start to really drag, julia is still on llvm 3.7, so does ghc 8.0.1. I don't think it's healthy.
I should also note that the internal APIs are not the problem for Julia. We usually pick those up immediately. Rather, doing validation for a new release on all platforms, reducing, filing, fixing any regressions, etc is what takes the time (in addition to only a few of us knowing LLVM well enough to do so).
Some folks in the commercial world pull all the commits from upstream all the time in order to not fall too far behind. It's a pay-me-now-or-pay-me-later kinda thing. Forces you to take the interface breakage seriously lest it cause other commits to queue up while you let it linger.
I believe that stability of the internal C++ APIs is a complete non-goal of LLVM/Clang.