I have a raspberry pi 3b that I've been playing with to see what ways/how I can incorporate it into indigo. For those that havn't tinkered with one yet, it's pretty easy and hard to mess up. I also like that with a small handful of SD cards, I can have one raspberry pi and each SD card is another experiment.
I did a build using raspberry pi light set in kiosk mode with airplay running in the background. It worked alright, but the chromium browser is constantly asking for an update (even though it's updated). But, when it works, it boots directly to a control page and has airplay running in the background for sending sounds or audio messages to it.
Today I tried a raspberry pi android build which I like. I found some instructions for it that worked like a charm and include the steps for installing the google play store.
https://pimylifeup.com/raspberry-pi-android-lineageos/
So far, so good. The raspberry pi boots directly into domopad and goes straight to a control page. Pushing speech to it works, changing control pages, etc. So, for around $50, you can install domopad and mount one of these to the back of a TV.