I will add some missing input values to my version of asciimathml.js and try to create a php version next - possibly with tables of input code in database.
A small comparison table of some current symbols in ASCIIMathML, LaTeXMathML (and Fallback script) & LiveTeX (LaTeX)
in http://korpelainen.net/site19/mod/resource/view.php?id=8
Rendering asciimathml/latexmathml characters is at least 100 times quicker than rendering LaTeX (loading that page lasts for ever) but one disadvantage of rendering unicode characters with javascript is that browsers need to have support for those unicode characters (fonts). We could try an optional solution too: to upload fonts (STIX?) to server with moodle and use scripts like in Facelift image replacement technique to render unicode characters from server as images if browser does not have the font installed http://facelift.mawhorter.net/examples/ - it requires just php and GD and moodle sites have both of them.
I am going to test during the weekend some other interesting things like Prince - http://www.princexml.com/samples/magic.pdf and http://www.princexml.com/download/
By the way - unicode picker can be easily added to equation editor as one more tab... it's already working on my local box. I should just pick all the pieces and send you a copy. 