Someone created an openHAB binding that can do TTS through Alexa: https://github.com/mgeramb/openhab2-addons/tree/3083-AmazonControlBinding/addons/binding/org.openhab.binding.amazonechocontrol
TTS support was also added to another big Alexa shell script:
It would be great to see this ported into HomeAssistant as a native TTS component.