Had an experience last night in Business (3D) on QF962 CBR/BNE.
One Y pax came forward to use the toilet (well after the announcement directing Y pax to the 2 toilets in the rear) and the CSA was in the way, she directed him to the 2 toilets at the back of the aeroplane however he kept walking past her and used the conveniences. I thanked her for trying to police it; but the curtain was still clipped up.
At service time, the crew in Y had let the curtain fall but not done the clips. CSM was serving by herself so did the clips/velcro. The other CSA was in the kitchen. A pax tried to undo the clips and velcro and the CSM directed them to the toilets in the back when they poked their head through. Thankfully they acquiesced and didn't try to slip past the cart (which effectively blocks the aisle anyway).
On my other J sector yesterday (MEL/CBR) it was open slather, but no bulkhead and curtain so full view of the cart blocking access to the forward toilets for much of the short flight.
I'm ambivalent about the access rules - allowing in cases of emergency yes (children, unwell etc), but most pax fail to plan toilet stops appropriately (at home, office, QC or toilets on way to plane), particularly on short haul (less than 2 hours). Some of us plan ahead and don't have any issue
My 2c worth, FWIW (probably not much :shock