Density functions in surface rule conditions

Density functions allow for much more depth & creativity than the current surface rule conditions, the addition of density fuction conditions would be very helpfull for worldgen datapacks. For example: With a density function that fills to a specific y level & some noise to specify x & z locations, you could have multiple (dynamic & customisable) sea levels! OR With the help of the biome surface rule, you could have your own biomes have much more detail & control of blocks used!