I used to use the aptly-named TouchBarDemoApp to use my iPad Pro 12.9" as an external Touch Bar, and it was amazing. It even came with a full-size Mac keyboard, allowing me to (theoretically) ditch my hardware keyboard entirely. (In practice, the software Mac keyboard didn't work with the system autocomplete, making it difficult to type with, but I digress.)
Recently, due to incompatibilities with Mojave, TouchBarDemoApp and its iOS client stopped working. The developer definitely isn't going to update this.
Could Touch Bar mirroring could be added to BTT Remote? Bonus points for a software Mac keyboard.