Thanks for the quick response!
I was thinking along those lines, too – I even do some of it on a small scale.
One simple way to version (and contain) shortcut names could be to have years in the root of the shortcodes directory and copy them forward each year to make changes.
But multiplying code in the shortcode (to provide different functionality depending on what version the page expects) or multiplying files in the shortcode directories (already a bit hairy) are both bad habits making my (relatively simple) site more difficult to use and maintain already.
So I’d really like to just break the older pages’ dependence shortcodes so I can eliminate/consolidate/simplify/improve the shortcodes in use for future pages.
Obviously this is not really an hugo problem, but a problem with the way I have chosen to use and abuse hugo. 
I considered copying the generated .html files over into the content directory to replace my .md originals. But I worry about them having the appropriate frontmatter and then I notice all the files would have to renamed from index.html.
So I guess what I’d really like to do is to render the shortcodes into pure markdown to replace my original .md source files. Or, perhaps more generically, to replace all my go {{ templates }} with the markdown they generate.