Synthesizing Grant Goldman's or Taylor Owen's voice from individual syllables rather than the current words would be difficult, if not impossible, and would sound unrealistic. The easiest way is to construct any words not available out of the existing announcements. This is easy to do with any reasonable good sound editor (I use Audacity) and if you have any particular requests for words and phrases I could have a go at making them.
I do not have the on-train DVA sounds (besides the limited number of recorded Millennium ones provided to me). If anyone is able to provide me with recordings or even better the original sound files, I can add them. An on-train indicator display is definitely possible, just needs a realistic looking LED display style font.
For stations that have or had not been opened, it's possible to cut together sounds to make some of them. The Sydney-Female DVA has ECRL stations already, and I've just prepared ones for Sydney-Male that will be in the next version (e.g. Macquarie Fields + Wiley Park = Macquarie Park, North Strathfield + West Ryde = North Ryde). The others would require actual recordings.