Any rotational system in which there is no rotational limiter could benefit from a non-contact way to measure rotation. This way if you over-shoot you don't destroy something like you would with a hard limit. Course you can do this with optical interrupters.
You could use this in fluid control applications where you need to measure the rotation of a valve whose body was contained in a vessel as well. Picture a magnetic stirrer.
It could be used in biomedical applications because blood is actually quite problematic to work with. Picture a value, a stent, or perhaps some form of implantable pump.
It could be used in aerospace applications for monitoring the rotation of apparatus through the walls of the pressurized environment.
It could be used in turbines for monitoring the rotation of the veins or turbine itself.
It could be used in fuel pumping environments.
Perhaps it could be used to measure the rotation of a fluids draining from a vessel if the fluids had something ferrous in them or floating on them.
It could be used to sense the rotation of 2 vehicles in a near contact situation.
It could be used in a variable compression or Wankel engine.
It could be used to measure the velocity of gasses.
There is a company that makes large RC car style servos with the magnetic encoders from Melexis.
It could easily be used in brushless motors.
It could be used in HVAC on vents and registers.
It could be used in security locking mechanisms.
If could be used to maintain timing in mechanical systems that engage and disengage.
It could be used in hydraulic or pneumatic motors.
It could be used to measure the rotation of a 2 part connector, solid or hollow (for hydraulic, pneumatic, or electrical).
It could be used in a rotary UPS to measure the rotation of the flywheel.
It could be used to measure the rotation of high power antenna elements.
Call MIT they can use if for this:
http://whatsnext.blogs.cnn.com/2012/...culpting-sand/
Bet you could use them in the countless LEGO models:
http://www.pcworld.com/article/25158...nt.html?tk=out
It has military application, but I'm not Tony Stark and we're not going to talk about that here.