But if your sabbath falls on on a Tuesday this year, Monday next year, etc. it's going to cause lots of trouble with store hours, work weeks, school schedules, and so on.
How is that any more the general society's problem than dealing with other religious events, especially "moving" ones like Holi or Ramadan?
For much of the world, one or more religious groups with a fixed weekly holy day constitute the bulk of general society.
Because the religious make up a majority of society (and it is apparently only going to grow due to secularism failing to pass on the idea that having more than one kid matters).
Secularism should not have to depend on number of children to grow. The idea is good enough and will find traction in children born to any religion.
Well, I suppose "How is your new datetime scheme our problem?" and "we have the numbers and we're not changing".
All muslim events such as Ramadan and Eid move every year and there is no issue.
That's fine for the occasional festival, but for something that happens every seven days, that's a huge adjustment to make.