Come to think of it, it wouldn't be bad idea for a headphone company that really wanted to make a Mainstream Ortho to start with something like an updated, upgraded SFI: design a miniaturized version of the T30 driver using NdFeB slotted disks with an Audezelike ultralight tensioned diaphragm, design it for mass production, and make the dipole sound a selling point. After all, 'stats are dipoles too.
And orthos are, in principle, simple. Orthos have quality control problems that must be mastered (tension, thickness of voice coil, machining the magnets for flatness, driver matching, etc), but once that's done, they're not that difficult. No high voltage, no tricky centering the voice coil exactly in the magnet gap. It's the initial investment in the tools required to monitor these new bits as they fly past that's the sticky part. A mainstream ortho can be made-- look at the Wharfedale, which still sounds good today. It's engineering a good modern design for mass production, then making that scary initial investment that's the trick.
As for orthos vs. electrets: There were certainly some bad electret 'phones, but overall, vintage electrets from Stax and Sony were clearly superior to contemporaneous orthos, which, as we well know, sound smooth but dull. The Stax SR-30 actually has bass, surprising for a Stax of the time. The Sony has even more bass. On the other hand, even these were expensive 'phones back then. The Yama Orthos were somewhat expensive, but the HP-2 and 3 were not too pricey. They didn't compete with even the cheap 'stats at their price level, so it's a little unfair to compare them.
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Though Orpheus'es are not bad too.
