The point about a static site generator being an ideal intro project is well-taken. I'm working my way through Practical Common Lisp right now, as it's recommended as one of the best CL intro books, and its intro project of an MP3 database is only barely relevant to me because I still have a stash of MP3s I started building up around the time of the book's original publication.

I struggle to imagine what might supplant the HTML generator suggestion in the future. If anything, its desirability is made more apparent by the proliferation of JS monoliths all over the Web. You can show students how quickly it renders compared to a corporate website or heavyweight social-media feed, use that as an introduction to performance considerations and profiling, introduce modularity by bolting on a more dynamic framework piece-by-piece...