That would be awesome to create, manage and perform text inside one app. Mirror it, choose the speed, control with apple watch.
You could build an HTML action to do all but the Apple Watch part. The action can use HTML and CSS to mirror and scroll text.
Howecer, prompting tends to be a destination, so while it may not be a single app solution, you may get a better range of functionality by using a dedicated app for each of creation and presentation.
This latter one is my own approach:
I use Drafts to draft my text and then a custom action to export it into a specific Dropbox folder with a specific title. Using PrompSmart Pro I can then import it - unfortunately it doesn’t auto sync, but it does now (since I created the action) import from other file locations. The fact I can use it to track my speech and auto scroll based on my speech means I don’t have to chase the text or manually scroll it - via watch or anything else.