After months of asking, Google have finally taken an interest in shipping code that is valid for execution. They've added .js extensions to their imports! Let's congratulate Google's engineers on implementing what they were taught on day one of their JavaScript education.
I'm not sure if this repo fixes anything else they got wrong, but I've only seen this repo in reference to the imports issue. If that's all this repo fixes, and of course if you trust Google to maintain the use of valid JavaScript, it may be best to direct this lib's users back upstream with a depreaction notice.