The only major skips that are allowed in NMG are ones which do not use unintentional bugs, and are instead as a result of raw skill (ie. Bunny-hopping in BTG Door Skip, or throwing the cube in Test Cube Throw) or simply by using knowledge of the game to use a, whilst unintentional, still non-glitch reliant method of completing the level (such as Ricochet Panel Fling or Turret Factory light skip).

Whilst the line to draw on whether something classifies as a "glitch" or not is hazy in of itself, it's hard to really make an argument that any of these allowed techniques classify as glitches. Bunny hopping is the closest you could really get, but it has long since been agreed that it's more of a result of how the physics engine works as opposed to a glitch.

Semantics aside, NMG is basically Glitchless. You can't pick and choose which tricks you want to be allowed and disallowed based on personal whims.

Bump? Still feel this would be a cool addition, world runs at least.

I wouldn't mind helping out if there's ever a slot free!

Yeah, I prefer being Super for the all coins run overall because collecting coins is a lot easier with the bigger hit box (most noticeable in stages like 1-1, 1-2 and parts of 4-1) combined with the damage boosting and the fact that you can also have a backup in case you do take a hit (getting an extra apple/shroom in 3-2 is pretty easy and not a big time loss).

I also timed 1-1 both with and without getting the powerup, and I think it comes to about the same time, so I think it's worth it personally (although it does make some jumps, like the one near the end of 2-2 a bit harder).

Sliding is actually helpful especially during 1-3: it helps you dodge the last fireball you see without having to stop moving.