I like placing lava on my structures. I'd rather have it not drip on me whenever I walk in one of them D:
You could still do that. Just build your ceilings two blocks thick. One block thick lava ceilings would effectively be another method of defence as well as a minor hazard while spelunking. "Hot" floors would work the same way.
Maybe 5 hearts of damage a second, so there is still punishment for digging down, but ot as much?
Woah there, buddy, I was thinking half a heart per second, or something more along those lines. Just an extra nudge not to dig up. I don't think even direct contact with lava does five hearts per second.