You always note the difference - I tought than moving from the 20mp m4/3 to 26mp X-mount will not bring too much of a difference, but I was wrong. Both in quality and storage requirements...
For some instances, 40mp would be very useful. For concert shooting, the ability to crop from 40mp to 20mp would be very welcome. But for "no crop" work, not so much.
One thing that was never explained (or tested): if you drop the resolution from 40mp to 20mp in stills, it is oversampled or line-skipped? If you don't need the 40mp for some work, a oversampled 20mp image could both bring less storage requirements AND (maybe) more color accuracy. This would be a very interesting alternative to me - albeit, if oversampled, probably would not diminish rolling shutter (could even increase it).
And for video, the 40mp sensor needing to crop to be oversampled in 4k was a HUGE bummer.