yes and no. things get expensive in low volume production. So the stub/ flange assembly is universal.
But! The Flange and the stub are an assembly, ei 2 separate pieces, so a longer flange or a spacer could be used!
the stubs are leaf on one side, and 25spline Subaru on the outer. SubaruGears makes stub flanges for the Subaru splines, both longe and short. So that should cover the differences in location and lengths for axles
It would pretty well have to be a longer shaft, so to run in a support bearing; an extension (female splined on the inboard end and male splined on the outboard end) would be more difficult and expensive to build than just building a Leaf-to-Subaru stub axle shaft to the right length. Anyone shifting the drive unit to centre the final drive portion in the vehicle will use equal-length half shafts, and would use the short stub axles on both sides, so they won't use the steady bearing or need the longer stub axle.
The extended length Subaflanges
are not nearly long enough to reach the stock support bearing location, and presumably wouldn't fit the bore of the bearing. They might be handy for their intended purpose, to place the flanges further apart to suit the desired combination of track width and axle lengths
Using the Subaflanges so all that is needed is a stub shaft with appropriate splines on each end seems like a brilliant design to me.