Oooo, what if a future release brought the chasms back, and they occasionally flooded with magma/lava?
Almost worth the great violence it would do to the FPS.
It would be fun to see some sort of horizontal magma feature again. Seems feasible to generate underground rivers of magma at volcanoes, spreading out and feeding magma pipes and pools. May be a bit difficult to work with the caverns though. Would like to see magma features get the irregularity back that they had in 40d. It would be fun if they were more like spoiler tubes that actively avoided open spaces rather than extruding straight up through them in a shell of obsidian.
Will be interesting to see what form they take.