A click track would need so much options, as the subdivision of a click, whether it should occur continously or only in some measures, or only at tempo changes, which sounds for which beats at which volume...creating a click track function would basically be re-creating all the options each staff already has.

So the more versatile, and already existing solution is to create a (maybe hidden) percussion staff which contains the click according to your preferences.

Finale already has a click track in the Hyperscribe tool. The user sets the beat parameters and already has control of how the the click functions. All that's needed is to include the existing click in the audio output of the score playback. I can see how this would be helpful for singers/musicians to use as a practice tool.

As Harald said, the user can create a click track of their own by using a percussion sound for the click.

In the meantime, there is a script for JW Lua that is available on the French forum "Finalisons" http://finale-logiciel-aide-gravure-musicale.eu/viewtopic.php?f=15&t=5118#p26367.

(you have to register).

The interface is in French, but not difficult to understand.