It would be nice if starbases that have a constructor in the defending fleet came up as "Upgradable Starbase" in the task queue. It would also be nice if this happened when a constructor joins a fleet defending a starbase. It is unlikely that many players dock constructors at starbases not intending to upgrade them, and they can always decide not to do it.
The thing is, on big maps it is very hard to keep track of where constructors have gone; you have to visually search the map for starbases that are defended, or go through the list. Both of these are time-consuming and not fun. I always have to tell constructors to go NEXT to the starbase, then move them the one hex in, then move them the one hex in again when they kicked out after the starbase is built.
You cannot simply search for starbases with fleets defending them because some of them might have actual combat fleets docked; you have to click on each one. And no, a tooltip will not help, because even hovering over every starbase with a defended icon will take a lot of time on big maps. Also, if the starbase has drones defending it, it will always have the 'defended' icon.