For this reason (and their failed Kickstarter) I've never really been into Mycroft. After all it's kinda the same as Alexa/Siri just a slightly more trustworthy party when they say they're not using your data.
I'm just not interested in alternatives until they can run fully locally (not necessarily on device, on a local server or docker is fine)
If this Leon does what it says on the tin it might be just the thing for me.
It allows you to use the Google text to speech API for more natural voices, which is a cloud product.
It is a yaml config to use on device tts instead.
Install is flashing an sd card.
I was asking about self hosting on their forum and they were like "just use our hosted service, you can trust us". That's not different enough from Apple/Amazon/Google/Microsoft so I dropped it.
But like I said this was a few years ago. Never looked again since.