Most languages do already support ok-fine grained recompiles (at the module level) and it's just many linkers that are slow (I keep hearing from people that this need not be). And actually some of them already do something that is called "incremental linking".
Even C compilers regularly compile 100K+ LOC/second, so I think there's not much to be gained here. Yes, complicated C++ can be slow to compile. Maybe we shouldn't write compliated C++ code to begin with? In the end, batch compile performance also matters.