I wrote this app to do some of what it sounds like you're asking (despite the name, it can be just a notification and not TTS if you want):
However, I don't have mode change as a "native" trigger. You could create a virtual switch that (momentarily) turns on with mode change and use it to trigger the app if it otherwise would work for you needs, since switches are directly supported. Though it wouldn't be that much work to add mode...