It would let you put perl code into your HTML files,
Where do you get that from?
Well, that's the whole point. It's supposed to be dirt-simple for the web developer to use and deploy, and it doesn't get any simpler than having an html file with a little bit of perl spliced into it that gets run when you use your browser to ask to see the file. It also needs to be nearly foolproof for the average sysadmin to deploy with their apache (my understanding is that this would rule out mod_perl).
Regarding what's compiled into or not compiled into mod_perlite, or what modules are loaded when: those are implementation issues that will probably be worked out later. Sure, it would be great if mod_perlite only reloaded modules if they've been changed. That sounds like a feature that will come later.