I'm not sure if it was that first video or i saw/read about this approach somewhere else (i'm almost certain that i heard about it years before that video thoug

I'm not sure if it was that first video or i saw/read about this approach somewhere else (i'm almost certain that i heard about it years before that video though), but my reaction was pretty much the same as Jon Blow's (though not so long winded :-P): aren't you just working around the borrow checker and making your own allocator with its own faux pointers via indices? Sure, it wont crash the game if your index is invalid, but you'll still access the wrong data - which can end up with hard or weird bugs and corrupted state (e.g. in savegames and/or editor).