Indeed, several people have pointed out to me that this idea has already been out there for some time, only it's been called "extension blocks", albeit not defined with as much detail. Started to read the discussions on it, seems very similar. Gonna continue reading to give them proper credit, but also to figure out why this proposal hasn't been greenlighted and what arguments could be used to showcase the benefit of its activation. I see it started in pre-SegWit era, maybe this time will be different because we have seen a successful SegWit activation, which is highly similar to the proposal in question, in the way SegWit was deployed.