My currently solution for cascaded Webpages:
1. For each Subfolder SUB in MAIN create a SUB.jpg
2. Step by Step create Webpages for every Folder:
- For MAIN use a Template with Subpages for each Picture (e.g. _Default – simple).
- For SUB use whatever Template you like.
3. Manually: Relink the SUB-Pictures in the MAIN-html to the SUB-htmls
=> Point 3 can be done easy step by step after each page creation: Set Targetfolder e.g. to C:\WebPage\original then rename thumb.html to Picture1.html (or whatever was the Name of the "Page per Picture")
Suggestion:
- Create -> Web Pages... is the simple way for selected Pictures.
- Create -> Web Pages Folder... opens an Interface for one selected Directory (or add this feature in the context menu for folders, as you did it for Start slideshow (recurse) )
- Web Pages Folder... needs:
- a Button "Set tree template" which will open the interface "web page Create" and let you specifiy the settings for the SUB.jpg’s
- a Button "Set picture template" which also opens the interface "web page Create" but lets you specifiy the settings for the normal Picturese. (in a first step use the same template for the whole tree und make only one button)
- The Button "Create" first checks if for each Subfolder SUB a SUB.jpg exists, then creates the Web Pages step by step: Use tree template for Folders with subfolders and picture template for folders without subfolders.
It took me 3 hours to find a simple programmable solution with less work for you... and writing it down readable... hope you can use it
... and hope it is something new 
Bruno