Building and gardening under ground and under ocean
I really like that there is no suffocation mechanic and was able to build a functional group of buildings several blocks under the ocean. It was a bit of a challenge setting up up to allow me in and out without flooding it, but it worked. What I didn't like was that I couldn't grow anything down there even though the area lights up with day light during the day through the hole in the ceiling.
It would be nice if I could at least set up artificial lighting to grow plants and even trees and even translocate animals under ground or in clear domes at the bottom of the ocean. (maybe glass blocks could be a crafting item that could form a dome if put together a certain way)
If we could build tidal energy or even geothermal energy production systems it would be possible to limit environmental impact by building in domed cities.
Of course, if that is possible, there would probably be a need to expand on the ocean importance. Algae, for example, could have a bloom cycle near farmland that uses nitrogen fertilizer taken from animal husbandry (but maybe farmland grows faster near the water to create a conflicting interest) and setting up a farm upstream can cause fish to die out all along. That could in turn conflict with the interests of players who do fishing. Maybe also allow players to set up fish farms by closing off sections of ocean, but if the waters are connected it could foul up the nearby water.
Building under the ocean would therefore mean competition for space, and farming can still leach into the surrounding waters causing harm.
Maybe building underground could provide a viable alternative to stopping the meteorite. Instead of forcing players to push towards high tech, maybe allow them to try and weather the storm so the world doesn't end, it just turns into a harsh winter that eventually gets better. This could create incentive for going under ground and pushing for renewable energies like geothermal power, but could create a conflict of interest as some players will want to form an underground commune while other players will try to stop it. If geothermal power tech could also allow someone to crack the core (beneath the bedrock) it could be a route to a doomsday weapon as well, maybe even creating a kind of Lex Luther scenario as one faction of players try to doom another faction while at the same time wanting to plan to restore the world after. Adding layers of social dynamics would make for some interesting outcomes.