Coldplay have a really bad history with pianos/keyboards.
Their early years they used a Kawai mp9000 (that's the sound we hear until today)
From AROBTH to MX they used the Yamaha GT-20 silent piano (no actual string in it)
But Yamaha stopped the making and the support for this piano and because none of these are road made they kept breaking. R#42 (Miller) has a blog about ending up with 5 GT20 pianos for one concert (normally there were 3, 1 main, 1 spare and 1 on the B-stage) and using them all!
During Ghost Stories they got some new Yamahas DYUS1E3 PE, full upright piano w./ strings and of-course MIDI capability.
They used them until the Superbowl (I remember the Yamaha piano breaking down in the St. John @ Hackney AHFOD concert). So from the and superbowl and now on they are using the Kawai - K300 ATX2 (always with a back up waiting on the back left side of the stage).
In the beginning of AHFOD they had also a Kawai on the B-Stage (going up with a lift) but probably Chris wanted something shorter so he would be able to look at the crowd.
Here come in the keyboards.
In the X&Y era a Guy was using a Moog Voyager.
In the Viva la Vida and Mylo Xyloto era they used 2xKorg KONTROL 49
But in Ghost Stories they went back to the Moog Voyager and a cut down Kawai MP8 (to about 49 keys).
Back in AHFOD we began with the Moog and the MP8 but later on they proved to be not so road worthy so we moved to some simple 49 key midi controllers (I'm not sure about the brand).
So today we have:
2x Kawai K300 AXT2 on (1 on the riser and 1 hidden as a spare)
2x Generic 49 key MIDI keyboards (maybe the Korg KONTROLs?)
B-Stage & C-Stage:
1x MP8 or MP9000 (I think it's cut down to about 66 keys not 88 nor 49)
Also there's a Kawai or Yamaha upright piano waiting as a spare in the B-Stage
On the stringed pianos apart from the midi triggering the kawai grand piano sound from the playback racks there are also 2xDPA microphones for blending in the sound.