There is already signals going to the Trent900 (the engine used) vanes. THere are vane actuation to change the pitch so prolly wire since there is already acomidation for such.
I doubt that that is the most expensive. RR always destroy their engines. One of their favoite tests is to take a frozen turkey, defrost and fire it at running engine to test for in-flight collisions (the dum-ass Yanks too this on board (P&W) but fired a frozen one at one of their engine's and completly destoyed it!!!)
Anyway what I am saying is RR/P&W/GE all test their engines to destruction. this time next year when the Trent1000 (for the Boeing 787) gets tested it too will cost alot - but shouldn tthat be in pounds since RR is British or at lest in € since the main engine testbed is in spain for RR)
Anyway that isnt the most exposive test.
The US gov'n and I think NASA wanted to test (since couldn't simulate) a wing rupture on landing (fully fueled) to see what is vulnerable and how to protect.
They took a 747 filled it with Fuel and dummies, lots-o-camera's and sensors and flew by remote control
The idea was to fly over these big metal poles to rupture the wing (where the fuel is) to the start the fire on final aproach, however didn't quite hit is square on and relly ripped it to shread's huge fireball, uncortolled and wasted data
https://www.alexisparkinn.com/photogallery/Videos/720test.mpg
here is a vid clip - all I could find. So that is is alot of test equip, a 747 (which cost a few hunder mil) and four GE engines... not to mention test data that was unrepestative - the data they could salvage....