I'm one of the authors of this PR, and yes, WebAudio's baffling lack of proper consecutive buffer queuing has been no small source of frustration. They seem to have put so much effort into adding effects nodes and other such things, but something as simple as scheduling one sound to play gaplessly after another can't be (easily) done. Requests for such support have been batted aside as unnecessary, which is funny considering where all the effort is going instead.
To do it properly would require just giving up on WebAudio's features completely and doing all the mixing in software via WebAssembly. Honestly though, if you're going to do that, you may as well just compile OpenAL-Soft with emscripten and use that, so I opted to just try to get the best out of WebAudio that I could. Hopefully it's good enough.