Anything is possible to add.
But the real question is who will write the check to pay for it?
The TMF does not turn a profit, and in fact, costs its owner a fair bit every year out of pocket to simply keep up. We are running decades old forum software because upgrading it to a modern version is simply not in the budget. So adding audio (and video which is also possible) are items that are equally unaffordable.
So unless Scrooge McDuck appears and drops a Money Bin upon us, we'll keep making do as we have for 23 years.
And I'd love to see all sorts of improvements, and audio in chat is not a bad idea overall, and I'd support it too. But life is what it is.
Myriads