You can always log a feautre request. However for a non-responsive projuect it is a breeze to add a slide number:
- Open the Master slide panel
- Select the Main master slide
- Add a text container (shape or caption)
- Go in Edit mode (F2 or double-click the text container)
- Use the X button in the Properties pane lunder Character and choose the system variable cpInfoCurrentSlide
You'll get the slide number on each slide autoamtically. >To delete it repeat the first two steps and delete the text ontainer.
Have a look at this blog, with lore ideas about using system variables:
http://blog.lilybiri.com/discover-slash-use-captivates-system-variables-part-1
For a Fluid Boxes project (can also be used for a normal project):
On the first slide insert the text container (in a fluid box if necessary)
Insert the system variable which I mentioned
Go into Timing Properties, and change to 'Rest of Project'
Check th eoption 'Always on top'.