I came across the need to have the HTMLModule generate 404's for pages that aren't present. In my case I wanted to specify my error pages in my Apache frontend that'll be connecting to JBoss through mod_jk2. It's a really quick fix(I think under 10 lines) but I wanted to see if anyone else wanted this behavior before I committed it.
just make it configurable, w/ the default value being "don't use" - then if other ppl want to use it in the future, the functionality is there.
personally, i think it's a good idea.