That would be nice. I think its balance thing - underground or not, good placed nuke will kill it. So it should be an option, but it should be costly - for one no loot from nuked base, for second significant drop in funds from that region - local politicians dislikes such treating of their lands... Also it could need special bombs to be researched first.
But also i would like to have option to airstrike landed UFO - if its very as grounded as one shooted down, its same ground target. But to not making it easy - UFO should have some chance to get airborne just before airstrike - so its random when you do that - or UFO is destroyed and you get similar loot as from airstriking shooted down UFO (or liitle more, UFO in this scenario is shooted at once, not twice and crashed so less equipment damage) or it gets airborne and airstrike failed.
