This would be a boon to indie RPG developers, since speech is a huge part of any modern game, especially RPGs, and would be a huge undertaking otherwise. Also, the quality of the speech generated is much improved since years ago, and doesn't sound anywhere near as robotic as it used to. I would think using synthesized speech would also give a much greater degree of control over mouth movements of models, giving a much more convincing presentation. I am by no means an expert, and perhaps the technology isn't as polished as I've percieved. But after seeing a blurb on TV about how far they've come with this technology, I couldn't help but think how useful it could be for game developers, and how much time/money it could save.
I came across the following after doing a quick googling of "speech synthesis c++":http://www.cstr.ed.ac.uk/projects/festival/
By the way, I've been looking to make a game for some time now, and have dabbled with one other engine while still researching others, and I have to say that Crystal seems to be on the right track with all the features it provides (the foliage generator has already got me drooling). Great work! Looking forward to seeing what the future holds for Crystal Space