I'll tell a story (like I always do) about my idea. So, I was on the Darkmere, and there is that room where the slime is simulated moving by moving up&down some blocks of slime around the ground. That remembered me of a video I saw once, I'm not sure which one it was, I'm thinking it was a Let's Play of Hexen, but I'm not sure at all, where the water actually waved smoothly. It was somewhere else, not on that waving room. If it was Let's Play Hexen, then I think it was on ZDoom. I'll see if I can find the video again.
It wasn't some extra complex ripple effect that it had, it was a simple linear wave thing, which looked simple and good.
So the idea hit me:
Why not do something like that for the Doomsday liquid surfaces? Maybe not lava, lava kind of looks like it should not be waving, but maybe it could work. It would add some more to the visual interest that DD already has, and would be a subtle effect that would make the world look a little bit more real.