Many thanks for taking an interest in the future of Showkase and for your suggestion.
Have I described something that exists? Within the Kosel theme?
Unfortunately, it is not currently possible to have an index page of gallery index pages (under any theme).
Showkase supports only two levels of menu items and gallery index pages can be only top level pages (listing gallery pages on the second tier).
If not, is this something that should be available to Showkase users?
I would certainly encourage you to post suggestions for future versions in the Feature Requests forum thread.
This keeps all the ideas together and ensures that they are not overlooked by the developers. Thank you.
How hard would it be to manually create create a page like this?
It would certainly be possible to manually create an index page of gallery index pages although knowledge of HTML (and possibly CSS) would be required.
If you installed Showkase in a directory named 'showkase' in your root directory and had a couple of gallery index pages named 'index1' and 'index2', then you could create a 'Basic' page and add HTML code such as the following into the text editor on the page (in 'Source' mode).
<div>
<a href="/showkase/index1/">Click to view first gallery index page.</a>
<br />
<a href="/showkase/index2/">Click to view second gallery index page.</a>
</div>You could expand this example to add a representing image for each gallery and you could style the page using CSS to make it more visually pleasing. (If you had only a couple of gallery index pages, then this might not be too large a project.)
I hope this points you in the right direction.