Different blocks instead of Stone for the upcoming underground biomes

In 1.18 we'll get underground biomes that can generate depending on depth and regardless of the aboveground biome, which is great. Checking the json files it seems like they can't dictate wich block is used as a base block, I mean, before caves are digged, ore blobs are spawned etc. It's always Stone, and datapacks can only change it to something else in the whole world, not by biome.

This is probably the biggest limitation of the current system because it makes it awkward/laggy to add underground biomes made of different stone types or even ice, dirt, sponge, whatever. Not only for datapack makers, but also for biomes added in future updates. Since the biomes are determined on a noise-driven block-by-block basis it shouldn't create ugly straight lines of different blocks, but I'm speculating here.

In case you don't know: you can make a biome generate a lot of "ore" blobs that are just granite, blue ice of anything else, and it will basically change most of the stone to that block, but it's still patchy and it makes worldgen lag noticeably, which is far from optimal.