This actually a pretty interesting take.
I see how it can work with experienced players ready for some experimental game, but indeed it's not something I'll do on another context for the following reason.
I don't know whey some people seems to strongly decorrelate the system from the rest of the game. The mechanic is a component of the game theme and mood and a good pairing Setting/System is important. To be cliché you're not going to use D&D to play Chtulhu unless you want to do a dungeon crawling agaisnt Mi-go
Many players don't have a feeling about which game mechanic they can come with
This kind of discussion works if you have a lot of time. If you're young and plan to play until dawn no matter what, sure it's fine. for a busy and married adult needing to have dinner with their SO and who plans to take the last train home to come back, you don't want to loose time with these less important questions
It was huge in the 90's with the everything you need in one book, while AD&D collections of book were too expensive for the broke kids we were.
I believe they're know at the 4th edition, and unfortunately switched to multiple books like many others publishers