Something I don't see coming from any blogger tool - a client side preview engine. I'd love to see some installable that gives me the ability to preview template changes offline. Perhaps it could cache my own site content, or just use fake stuff (Lorem ipsom?). What I'd really like to see in it is the ability to add [fake] content dynamically (as in a live preview) to test out various stylesheet elements or WP template tag-code. Maybe something could be put together using the php.exe from a 5.x distro with iSQL. I'm just brainstorming. Really though, surely this is surmountable!