So seeing as digging underground, mining for ore and making underground bases and bunkers has been discussed a lot, it’s obvious people would enjoy such a thing (i know i would, moreso for the mining than base building ) but obviously it would be difficult to do it without making the game voxel based, and being voxel based is 1: unoriginal and 2: difficult to make look anything better than not quite ugly.
We all know how much fun 7DtD is, but the graphics are less than beautiful and really bad performance wise.
So to get around this i think one idea would be to do something similar to RuneScape or Haven & Hearth and make it so you can only mine in a grid, and only in separate underground worlds.
You can access these underground worlds via caves or player-built mineshafts, which go one layer deep. You cannot dig upward or downward, or on the Y axis, you can only dig tiles of rock on the Z/X axix. You must build additional mineshafts which allow you to travel (teleport) to another mineshaft directly one layer higher or lower.
Anything can be built or performed underground that can be done above ground with the exception of farming and such things that need sunlight and whatnot.
The deeper you go, the harder the walls are, the more advanced tools are needed to mine the walls, but the more ore and such you can find. (If perhaps dungeons or similar things are added you would have higher chance of running into burrower zombie/zombie mole/whatever dungeons the deeper you go.)
You probably couldn’t rebuild walls or place dirt/stone, especially not on the surface.
Obviously the biggest problem with this idea is that all those extra layers (worlds) would need to be rendered server-side which could really hurt performance but i just wanted to through one idea for digging underground out there that wasn’t just make the game voxel.