There are many arguments for calendar reform, one of which argues that we should set up the calendar so that every date always falls on the same day (Invariable Calendar) .
If this Invariable Calendar were adopted, then the day that we celebrate as Shabbos now, would not necessarily be a Saturday. In fact, if I understand what they are proposing, then the days that would be Saturdays under our current calendar will move around from year to year and maybe from week to week.
Although I doubt such a reform would ever be adopted, I'm curious what we would do halachically if it were. Would we change the date of Shabbos so that it still always fell on the date that was designated Saturday in the calendar, or would we have to figure out a way to keep Shabbos on the date that would be Shabbos in the current system? (The former might be impossible, because the Invariable Calendar adds a day once a year that has no day of the week. So, if we switched Shabbos to every Saturday in the new system, then at least once a year there would be 8 days between Shabboses.)
The answer to this question depends, I know, on how one rules on this question: [History of Shabbat: how (or) did they count to align with 7th day of creation?