Did you consider removing or hiding landfill and its technology?
In effect, that is kind of what I’ve done. Deep landfill is prohibitively expensive to use for anything significant but I like that it’s still there as an option in case there’s this one tile of water in your way or something.
However, I like the shallow water as a mechanic: it is more realistic and it’s allows for a waterfill that doesn’t block biters so isn’t overpowered. It is also useful for boats as you can walk right up to them near the shore. But my understanding of cargo ships is that it’s basically impossible to load or unload them without landfill to make a jetty (or I suppose waterfill to dig into land). So I thought it shouldn’t be too expensive to make this jetty as long as it’s in shallow water. You also need (cheap) landfill if you’ve got a line of walls ending at shallow water: the biters can walk around the walls unless you landfill all the way to deep water.
So, I’m pretty happy with the intersecting mechanics of ships, deep/shallow water, deep/shallow landfill, and canal builder.
I could certainly move around the tech positions: normal landfill needs to stay at green science to go with cargo ships but I could put deep landfill somewhere in blue science or even later…
I like concrete as an ingredient, at least for deep landfill. Potentially iron sticks as well (although refined concrete already includes that). I’m not currently coming up with anything that would fit, so probably stone + (refined?) concrete. Maybe low density structure, or perhaps wood to give it another use?