OK, so i see I made some wrong assumptions.

The new 12 speed uses the same Sturmey Archer 3-speed hub as previously. The difference is the derailleur.

Disk brakes won't work with the electric hub drive, and in general apparently they interfere with folding.

So all that seems out.

There's an H6L electric on FleaBay which might fit the bill. The P-Line looks nice but the better components are all lighter, particularly wheels and tyres, which is maybe not good for my application, which will involve hauling fairly heavy loads of groceries to the boat.