did some experimenting and based on the current terrain if i bitpack it and then gzip compress it, a chunk averages 170 bytes, so i could store a world with 1024x1024 chunks (or 16,000 by 16,000 blocks) in 2.5 gigs at full resolution
or a world the size of gta5's map (5120 chunks squared) in 66 gigs
that's not bad at all tbh given that isn't occlusion culling underground chunks and is at full level of detail