since i play a lot on jungle maps, i would like leaves to not be a hard block you want walk upon. Nothing really realistic or fun with being able to walk OVER a forest, jungle should be hard to cross.
Make it kinda like cobweb: you can move through it, but at lower speed
Doesnt have to be as slow as cobweb, but annyoing so players would rather opt for cutting paths.

Additional idea: ozelots can trespass without speed nerf (like a jaguar being able to move through dense jungle without effort.)
could extend to some mobs having that ability as well, to make jungle more dangerous. RN its the easiest part since nothing spawns there really.

Impossible without modding the client.