I came in expecting to hate this and actually love it. You've clearly put time and effort into organizing these ideas. The nether really does need improvement and this addresses some good things. Specific criticisms:
-the "gloomroot flower" is overpowered, and its effects don't really make sense. It should be redesigned.
-the giant "wayfarer" is too strong and too big. It's a good concept but the unused Giant mob shows hitboxes REALLY don't like to be that big. By shrinking this enemy somewhat I think you have a solid enemy.
-the "enchanted collar" size increase should be less than 2.0x, probably around 1.4x
-the "ghast egg" doesn't have enough utility, and rendering ghasts passive seems like a good way to nullify part of the nether.