Fast Company: Google InnerTube project to retool YouTube is a great article talking about a lot of the more recent changes that Google has been making in order to fix some internal development issues and make YouTube more of a competitive destination for watching content.
It's funny hearing the talking about the mess of Frankenstein projects that had grown up over the years. It seems like every project that's in continuous development turns in a Frankenstein. It's always a constant battle to keep a project clean. If you don't, then up you end up reaching a point where you almost have to over from scratch to get the project where you you need it to be.