One thing that has always bothered me that I'd like to get considered in the realm of IPS4 is documentation.
I have one example and thats it.
I recently got a new development server to Nginx. My live server consists of 1 wordpress blog, 1 xenforo site, 1 invision power board site.
These were my Google searches to prep for the changes and their yielded results
"wordpress nginx rules" - http://codex.wordpress.org/Nginx
"xenforo nginx rules" - http://xenforo.com/help/friendly-urls/
"ipb nginx rules" -
No official documentation. I know you don't support it, but its always helpful to have a nice starting point when writing rules. After reading about 3 separate threads on IPS about Nginx, I finally wrote my own modified rules, which I've yet to test since I'm too nervous to make the move. I'll have to setup a test site and mess around, but thats besides the point.
Hell, Xenforo even gives out IIS rewrites and lighttpd.
I personally think this could very much separate you from the competition, especially as times are changing. More and more people are moving away from the basic mySQL / Apache to things like MariaDB + XtraDB, or lighttpd / nginx / varnish / squid.