Unless there has been major changes for T:ANE, there won't be any changes to TS12. Sounds are one of those things that kind of took a back burner position for Auran & N3V Both. They focused on making a good looking simulation and World Editor/Creator.
If you really are working to become a Game Audio Engineer, then a big part of that is incorporating your sounds into whatever framework the game has to work with. If you want to improve Trainz, work with what's given and try to find new ways to improve its sound without eating too many system resources. Scripting sound is just as important as Capture and Playback quality for instance....
Ultimately, I kind of agree with you, a lot of the sounds in this simulator aren't that great. The best are usually the result of Payware Firms/Groups spending alot of time trying to Monkey with things. I too would like to see improvement on this score, but I'm not holding my breath, and ultimately am content with what I have and with what N3V/Auran are likely to continue providing....
Whatever you decide to do, good luck,
Falcus