For example I want to send my Gravity Trampolines to a coordinate in defense so that I can teleport to it, 
but I do not want them to arrive a long time before I finish recycling. Right now I would maybe send at 50% speed 
What if they get close to the coordinates and I realize that it is going to take me a little longer to finish the recycling?
It would then be a nice feature to be able to slow them down just like we can slow down the attacking fleets in increments of 30 seconds at a time.
 
http://prntscr.com/lnaygh
also it would be nice if all these buttons would appear here as well http://prntscr.com/lnbd44

If you really wanted to add more control to the in flight fleet you could even add a feature that allows us to
change direction and send to new coordinates as long as we had the vespene with the fleet to do so.