Whoever thought to include the theme ID in the deprecation notice is brilliant! (And it’s amazing how things like that can take so long to become “obvious”.) Maybe it was @david, at least he committed it.
(No offense intended to the theme in question…)
This saves me on the order of an hour figuring out where to look. (Perhaps a slight exaggeration.)
So fantastic.
Yup! I must have spent so many hours over the last few years manually digging through backtraces to identify problem theme/plugins… and then it dawned on me that we can have a robot do it!! 
None taken. 
Btw, I’ve pushed a commit replacing this.container by this.register to get rid of the warning. @pfaffman can you try and confirm that it is gone?
Awesome! That did it. I was going to try to submit a PR yesterday but got in a fight with git.
Thanks!