I do'nt use web preview neither (who still writes static html ??) BUT I would if the web preview could be used as the output of a custom TextMate command. One could the call a script whose output would be well designed html to display a complex error log, for instance.
Just my opinion but why not let your command do this instead? you could pipe it to safari or end in `open -a Safari /tmp/error_test.html`
I do such a thing currently. I'm just pro the cool factor :-)
While I'm at it .. I would also vote to not put too much development into WebPreview since Safari is only a command-tab + command-R away.... unless there was a feature like SubEthaEdit that did WebPreview in realtime as you type.
But at the same time, I agree with you. There is a lot to be done (the "refresh" bug drives me nuts) right now before the developers should take time for new features (expect maybe the function popup :-) ).