I can’t recall the site but I remember seeing a drone that had some sort of pneumatic seed launcher that could shoot the seed deep enough into the ground.

Australia is using drone planting on steep slopes to revegetate native trees after selectively killing invaders.

You're correct that the survival rates are much lower than hand planting with a shovel, this is offset by dropping seed embedded nutrient "balls" that do better than seeds alone and by saturating with expectation of low survival.

Cost-wise it's looking to be cheaper than the alternative of slow dangerous scrabbling rope work to lant by hand.

The trials will tell.