Hm... I think you are being a little pessimistic here.
I recently wrote a "jukebox" in an hour to play music with my
linux PC. Just text-links to bash-scripts that run for instance
"mpg123 xxx.mp3" or "killall mpg123" (to stop) or "aumix -v 80" (to set the volume).

The reaction time on these are instantanious. I use an iPAQ with the standard browser, and the redhat standard apache web server. (802.11b equipment from cisco/d-link)

Each shell-script again does an http redirect back to the
"indexing" page.

So, unless there is something I don't know about, I can't see any reason whatsoever that this should be slow.
I don't know the empeg/displayserver internals, but if there is some "startup delay", this could be solved (of course?) by running a displayserver-like process, and then providing
"entry points" for these http requests.

If I had the time and the sourcecode for displayserver, I'm sure I could do something like that without much pain.

Marius (Escort Cab + Mark II)