Not yet. The problem is that Quest 5 games run on more platforms than Quest 4 games originally did - so we can't simply use Windows SAPI to generate speech, as that won't work when games are played in a web browser.
However I just came across this:
http://hacks.mozilla.org/2011/08/speak- ... n-the-web/ - so it may not be too long before this kind of functionality is available everywhere. (In the meantime, you could embed speak.js using Quest's existing Javascript integration functions, but this would still only work on Firefox and Chrome)