Cues seem to refer to instruments - not to players.
As cues refer to an instrument that is actually played at that moment it could be better to refer to a player rather than to an instrument.
Just a thought…
Actually cues are referring to one stave of an instrument rather than an instrument only, for eg the right hand stave of the piano. We have chosen this approach, because in the majority of the cases cueing is happening from one stave to another stave. It also makes easier to handle cases where for eg a player plays two instruments simultaneously.
I wonder if you have an example, where cueing a player would have some benefit over cueing an instrument stave?
This obviously does not work in all situations, but if you are composing for a small chamber group where everyone knows everyone else, you can rename the instruments to the players names. If you want, you can make the full name something like “Flute - Fred” and the short name “Fred”, so the first system has both the instrument and player’s name and the remaining systems have just the player.
Thanks for your comments. András: It was in a situation, where I wanted to demonstrate Dorico’s marvellous cueing-feature to some of my music colleagues: I opened a bigband-chart I had written in Dorico, then clicked a bar in a trombone stave and wanted to cue the lead-alto sax-players part. So I typed “Alto Sax 1” in the pop-over but nothing appeared… 
The reason was that the lead-player held a flute in those bars. Not a big deal to change the cue, but that led me to the idea that there are situations when it would be easier to make the cue refer to a player.
FWIW, I would have found strange that the guy holding the flute could be the source of an alto sax cue… At least your demo did not show something impossible in the real world! (or did I miss something?)
In this case if cues were referring to players, it probably would have created a flute cue instead of alto sax. But the problem would still exist that if cues refer to players, what music should Dorico show in the cue if the instrument has more than one staves, or the player plays more than one instruments simultaneously.
Hi András, thanks for your reply. I agree - the concept you have chosen is better in almost every situation.