I don't know much about app inventor. I first of all would encourage you to join our upcoming Thing Event which will unveil I believe our mobile strategy.
Looks like app inventor has a component called WEB? that can do GET and POST requests, I would use that to get the data from Thingworx to your app.
I'll check the Thing Event for sure as i'm really waiting something of Mobile. You are right app inventor with web can pull data from TWX i already did that and worked. The put/post is what i'm working now and i dont know what is the structure for the REST API call tu put the inputs... is in the headers? separated by & or where do i state them. Tests with postman work wll but there i cant see where the JSON to push is added.