I always get up with the light so I think 4am would be too unreasonable. Especially if most cafes remain closed for hours still. 5am is tolerable.

As for winter, an extra hour of dark doesn't feel like a huge deal. When I commuted in the winter it was often happening around 6am while still dark anyways.

I have a feeling people's morning habits will change a bit to compensate for the darker mornings though. So I think it'll work out in the end.

Where do you expect the premature deaths to come from? Rush hour traffic in the dark?