Make Sunday part of the working week
Now there's a novel idea! It's something that's long overdue, but the appetite for it from the companies side seems non-existent.
To the best of my knowledge, ScotRail have never under NX, First, or Abellio seriously discussed this with staff / trade unions. The staff, I'm fairly certain, for the right sum of money would accept it. The issue, as ever, would be money - and in order to make an acceptable offer it would need to be a greater add-on to the salary than the current monetary value of average booked Sundays, which for most grades is 15-20 per year. Personally I'd be very happy to work a few more Sundays per year but get an extra rest day in their place, along with the higher pensionable salary. A nice side effect of Sunday becoming part of the working week is that it would make rosters far kinder to staff; presently Sunday doesn't exist, so the rules regarding rest periods 'where a rest day intervenes' don't count, and as a result its very common to work 1600 to 0100 on a Saturday, and then 0400 to 1300 on a Monday. As you can imagine, that isn't at all conducive to safety critical staff being at their best come the Monday morning.
Sunday becoming part of the working week would mean that change from lates to earlies taking place in midweek over double rest days rather than on a single Sunday.
The main benefit to Sunday becoming part of the working week is of course to the general public, where the train operator has the same resources available on a Sunday as they do Monday to Saturday, and can thus provide the same level of service if required.