Currently the only option for TTS output is the action> on-show etc which is somewhat restrictive.
I was wondering if the same native wa functionality could be added to the conditional section since the only way possible is running a custom code that calls C_VoiceChat.SpeakText instead.

Also a secondary thing would be the possibility of controlling the volume of tts called from the native wa functionality since it seems to always use 100.

You can use TTS via conditions in the same way as actions.

For volume control, at the moment there are no plans to add that.