I wonder if the adjustable seat just has a different base frame from the non adjustable type ,but shares the same upholstered part of the seat. If so the base frames might be interchangeable as a nut and bolt job.
If so Honda could, if they chose, supply just the adjustible base frame as a dealer fitted option. Save on bulk and shipping costs. Wouldnt be cheap though as there is probably a lot of work what with air bags and stuff. Maybe the necessary frame parts are already available as spare parts for repairing faulty mechanisms.
Far better to have had it as standard, rather than trying to save a few grammes in weight and a few yen in cost differential. Or as an optional extra, although this would complicate vehicle availability. It could end up being like some Ford models where they say there are so many possible option permutations there are no two cars alike.
To be fair Honda are not alone in this type of cost cutting.
Someone might eventually make an after market option. You can already buy simple universal height raisers that might work on some cars such as spacers and longer bolts to raise the frame 2 or 3 cm off the floor and modified seat rails. But whether this is feasible on Jazz/crossstar/Hr-v I dont know. There is a lot of wiring, airbags, petrol tanks, Plastic mouldings and stuff. I doubt a honda dealership would even consider doing the job.