Currently the biome/ocean/level configuration lets you define a Y-value at which water can be generated. This is a single value and applies to the whole erosion.
By adding an optional noise-equation (or any other implementation) this could be further improved (e.g. for making realistic rivers, see attached image).

Like I was saying in Discord, this will most likely be implemented as an optional alternative to biome.ocean.level, rather than a full replacement.

Specific implementation ideas:

• Add an OceanInterpolator that either takes the constant level, or the interpolated level, and interpolates between samples & biomes
• Ensure that interpolation distance is customizable, especially inter-biome distance.