The play-by-email mode was broken to the point of uselessness in Civ5 and I don’t think they fixed in it in 6 (you had to have an always-on Windows desktop system running the server, and because the game logic was integrated into the graphics engine you couldn’t run it headless, and then on top of that there was basically no working system to coordinate active DLCs between players so most of the time people couldn’t join even if you did get the damn thing running) so my friends and I tried once and gave up. I would love for 7 to have a robust PBEM system so that we can play together without needing to spend hours a week watching paint dry while everybody else plots their turns, but I’m not holding my breath.
The average American house on a basement will have something like 40 m^3 of concrete in its foundation. If all of it could be utilized, that’s still ~12kWhr of storage capacity. Nothing to be sneezed at.