Wow, such ELITE songwriting skillz!
I actually sang (and played organ) on this once in a one-off amateur expat band in Tokyo.
The chorus is too high for my register so I rehearsed the whole song in a lower octave, but on the night I accidentally started singing the verse in the original key (thanks, stage nerves), so I ended up having to sing the chorus at a lower octave than the verse. But overall it probably wasn't much worse than the Chris Martin live cover in this video.
Very interesting to hear the demo.