As someone on a so-called "committed Sunday" roster, with no incentive or pay enhancement other than flat hours worked as overtime, I'd gladly see Sundays added properly to the working week for nothing more than the equivalent money added to salary that the current booked number of Sundays brings. Partly because it would also:
1) Mean that I could use annual leave to guarantee book a Sunday off, rather than relying on arranged cover or waiting for the roster to appear a couple of days earlier to know if I'm off,
2) End the ridiculous and quite dangerous practice of being rostered to finish at, say, 1 a.m Sunday morning after a week of late turns, then back in at, say, 3.30 a.m Monday morning for a week of early turns. Currently allowed because "Sunday isn't a rest day as it's not in the working week" - therefore the minimum of 36 hours rest between shifts when a rest day is rostered, doesn't apply. How ANY member of safety critical staff is expected to do this without being fatigued and possibly unfit for duty is beyond me. The ORR certainly don't recommend it, but theirs is guidance only, sadly.
However I do get that for those who work a significant number of extra Sundays over and above those booked, that solution would result in them losing earnings: however overtime is never guaranteed and so this is not a strong argument against bringing it into the week. The bigger argument, as mentioned many times before this post, is the extra cost in staffing increase.