I feel like Swamp Biomes are little lacking with atmosphere and flora/vegetation, but one thing that i especially think needs to be improved are the holes as seen here (not the pond in background)
So the idea is not to remove the holes or water, but to fill them with new layer/slab like blocks, that can submerge under water. The blocks could possibly have similar behaviors to soul sand, slowing down player. So instead of deep gaps where you fall in they'll be basically puddles and mud that slow you down
I like the idea of quicksand but completely disagree with both posts on removing/replacing the gaps. Do that and it will just be like every.other.biome. It should be a little treacherous. Minecrafters can't have everything on a plate and made easy.
I think henovida's idea of replacing with no slabs/layers would make it too easy to get across, but I do like your idea of quicksand. Maybe a mixture of both holes and quicksand personally rather than removing them entirely. There's also the danger of "Oh I'll just go around it" - even if it is a longer way round, could be an easy escape. Yes you'd be more vulnerable to mobs but isn't that the case in most places?
It should be difficult to get across (Hence the support of quicksand) which is why I agree with your post but - it's more the implementation of it. I would rather you would have to try and go across it (Quicksand and all) than around it. Maybe more sugar cane dotted around just to add to the quicksand to make it more swampy.