What do you think of these?
https://www.kickstarter.com/projects/121539746/screenstick-sensitive-joystick-for-tablets-and-sma
Each set comes with both stick attachments, so you don't have to choose between them:
They're not "smart", just joysticks with a conductive pad on the bottom. They seem to be attached with a rigid piece to two suction cups on the side, holding the stick just above the surface so that when you tilt it, the pad touches down.
I actually find this more interesting than a smart joystick, if they work well! The design looks quite nice. At $30 USD for a set of 2 shipped to the USA (early bird price), and delivery quite soon, I decided to give them a shot! However, I'd love to hear what others think from the images / etc, or if there are other competing products that might be as good or better already on the market. What appeals to me most is that these are so simple - the devil is really in the details and if the execution results in a product that functions well.