TL;DR
You can fast replace compatible entities when you hold one in your hand; it would be nifty if you could (logically) do the same if you are placing a ghost as well.What ?
If you have an inserter in hand, you can fast-replace another inserter; if you run out of inserters, and start placing ghosts, that stops working.It would be nifty if instead of getting "inserter is in the way", you would instead plan to upgrade the inserter with the inserter you're holding a ghost of.
Effectively pretend that a ghost is also an upgrade planner that plans to upgrade anything compatible to the ghost in your hand if there's something in the way.
