The tech and crazy cuts you refer to are as unintentional as the oversights and the Maro Kart 64 tech. While some of them are cool, it is apparent that Rev is built around the multiplayer ecosystem and makes it so that you're not forced to play one way in order to stand a chance. For instance, if you raced with a friend that always wants to do the Grumble Volcano exploit on Mario Kart Wii, you'd stop wanting to go to Grumble Volcano eventually, right? That's what it feels like playing with certain people on certain maps and it's never enjoyable in the random pub environment.
I make mention of this in my original reply. Grumble Volcano skips the entire track, that's no fun besides flexing (like Wario Stadium wall-jumping at the start of the course). Tons of gaming's best moments come from accidents, oversights or exploits; Skiing in Tribes, Wavedashing in Melee, Coptering leading to Bulletjumping in Warframe, and even something like Snaking in MK DS (while it added a moderate skill floor to the game, it also made it far more interesting and skillful to play). Rev should seek to legitimize oversights first, rather than just strike them from the record, because it's taking cool and fun things that weren't intended and throwing them into the trash instead of building upon them. Some things obviously need to be patched (checkpoint abuse, the missing collision on Canyon Rush that I mentioned earlier, unfair cuts, SPB skips like Daytona and Paradise Hill). Refine before refusal if possible.
Moving the 2nd item set to the parallel jumps would invalidate their usage on the last lap, though. Most 4+ lappers make it a point to leave some space before the finish line to accommodate for one last item on the last lap.
Having every other lap work better is a worthwhile tradeoff for the last lap's last item set being a little too close to the goal, I feel. That said, the first item set should just be moved up to before the jump, and the offroad section be given a slope-hump to prevent lawnmowering (never, ever use Glue, that's just bad design that unduly punishes players who get bad luck).
Actually a cool idea but overall the bridge is still way too strong of a cut to leave in. Outright disabling it on the 3rd lap just means that it gets turned from a catch-up shortcut into a pretty-much-guaranteed-to-win cut if you manage to take it on the 2nd lap instead.
Then it simply needs further refinement. Make the bridge go to the end of the cliff instead, thus making it a V instead of a straight line to the finish, thereby adding on some time to traverse. There's plenty of ways to fix this cut that I can think of in a few minutes of brainstorming, so just walling it up feels really lame.
Grand Metropolis' item sets are apparently actually leftovers from KartZ, in the sense that it wasn't lessened or put in places that don't invalidate a set. For example, the first item set is generally useless and is usually only taken to midair snipe at the elevator. Why go outside the floor that boosts your speed to grab an item when there's another set right after the elevator? There's also no real usage for shoes at the 4th item set (right after the blue and red paths; just before the path with a blue line through a red path) and is mostly just for burning some speed. Rev's approach for the item distribution is to spread out and lessen the item sets so that you've got time to use every item as best you can.
Most players go for the outside item at the start because an item is worth the extra second or two. They're especially useful for people trying to catch up since a set of shoes or Invinc more than makes up for the slight time loss. Even then, since Rev seems to have a frankly misplaced distaste for Speed Or Item choices, I didn't suggest keeping those ones. The problem with the reduction from 5 to 3 is that it makes coming back from bad luck extremely difficult, especially on a track like Metropolis where being hit on the backwards conveyors is a *huge* time loss. This is further exacerbated by the increased presence of speed boosters in the ending section as opposed to yellow springs (which had their own issues, admittedly), which invalidate catch-up items besides Grow and even offensive ones like Jawz. 3 item sets would be fine for a three-lapper (9 items total), but on a two lapper it needs at *least* four sets (8 total, as opposed to a mere six), although one of them could be an outside item set that's meant for catch-up mechanics.
The "building rooftop cut" is, again, another infamous oversight of the vanilla maps. This specific cut has made Grand Metropolis undergo several map updates throughout the patching phase in an attempt to fully remove it, as you already know. People finding ways around that, as well as the difficulty of said skip, doesn't mean it's any less unintentional. It is still pretty strong to do in a netgame, and that's a pretty good excuse for it to not exist in Rev.
The thing about the rooftop is that it's only usable once in the race, only at the very start of the lap, isn't that fast in relation to the normal track, and in vanilla means you miss on a potential item set. This is one of those cuts I'm referring to when I think it should be legitimized. Removing the death plane and making the roof off-road would keep it exclusive to boost items and thus could act as a catch-up tool while not being exploitable for end-of-race major upsets.