This is a speculation thread, and surely something for those who want to discuss hypothetical stuff:
In 1982, Apple released the //e, knowing that the /// was dying. At this time, they had a large inventory of Disk /// units that were unsold.
Why did they never make a Disk /// controller card for the //e?
IMO, It would have made financial sense, and would have provided up to four daisy chained drives out of the box. As far as I am aware, you would only need a few extra signals (drive select), and you would be able to send those to the card with ,dx commands; plus, ProDOS could have supported four devices instantly in the same way as SOS. (Although I do remember that proDOS only came to exist because one key developer spent a lot of their unpaid time porting the disk OS part of SOS to the Apple II.)
This said, I am curious how hard it would be to implement a Disk /// controller for the hardware. Perhaps I am overlooking something, but the main signals are identical, plus four pins IIRC for device select. They could still have made the DuoDisk, but it would have used /// style daisy chaining and supported two DuoDisk drive sets off of one card.