You need the most powerful brake in the most controllable hand, and for most that’s the right hand.
I think the difference depends on what side of the road you ride on and which hand needs to come off the bar signalling a turn. Rear wheel lockups being more controllable one handed than front wheel lockups. So for UK, signal right, left hand has the back brake. Opposite hand in Euroland but the hand on the bar has the back brake.
I asked about swapping Shimano M/C’s over on the bars. This would mean the bleed port would be upside down, not that this in itself would be an issue. But… internally, after taking the big M/C cover off, they are definitely made to be one way up, not the other. Upside down they would ingest the small amount of air in the M/C.
Swapping would be a hose change, not a lever change.