We started a split shift for a really busy oncall and it works out really well. It's Th->Tu, Tu->Th. So basically weekend+2 working days vs 3 working days.

Expectation is you are 100% oncall during the working day, so it works out pretty well between weekend vs non-weekend shifts.

I much prefer the shorter shifts to a full week. A full week on-call usually means delaying important project work, etc. for a full week.