That looks really good and I love that they're so small! However, I do not like paper/cardboard boxes at all, because they damage so easily and thats the whole reason I'm switching to UGCs in the first place.
The reason I love the idea of N64 mini cases (and SNES mini cases) is that if you have a retarded game, say Madden 94, Madden 95, Madden 96, and Madden 97, do you
really want to waste that much space with a UGC? Or just place it in another formatted cover? Seeing that N64 Minicases are printable, you still are able to store your cardboard cases, and cardstock works fine with them. Nothing lasts forever, even the UGC's break after useage.
As for your boxset idea, Metal Gear Solid (essentials Pack), Resident Evil (pack), Mortal Kombat (pack), Devil May Cry (pack), Hitman (pack) - are the ones for PS2 that I can think of that already have your "boxset" idea (or atleast a type of boxset that I am imagining)
PS1 games that have a boxset are - Crash Bandicoot Collectors Series, Spyro Collectors Series, and that is all I can think of.
Would love to see a nice printable version of boxsets for slimline cases.