One minor note. Neodymium is VERY strong in the right alloy for a magnet. And as a result can be Dangerous to handle. Pinch your poor FINGER between 2 of those bad boys and you are in trouble. Usually painful. Since it is a Rare Earth, you can have trouble actually identifying it in samples of OTHER rare earths. And at one point China was a major supplier, was working the price / demand curve brutally.
Neo is also Brittle, IIRC. This doubles the handling issues.
I've tried to get some traction with Magnepan to make drivers with Neo magnets. VERY strong means you can space the mylar further and still have higher sensitivity. But you also need a much stronger (heavier) magnet structure and in the case of the 20 series, which is a push/pull design as opposed to single ended, you can really have strength issues. Not to mention Medical since some implanted devices are sensitive to Very Strong magnetic fields. This ain't Ever going to happen.
A Possible 'work around?' I've seen some Field Coil speakers which sounded wonderful. Using a seperate power supply for an electromagnet, you do away with Permanent Magnets altogether. This is probably as expensive as it sounds. Or Worse.
Magnepan MG1.6qr HSU Research VTF-2 MK3 2x Parasound A23 Parasound P5 Cambridge Audio DACMagic Plus Sony PS3 x4 @3foot runs of 10ga Belden speaker wire. GRADO SR80e on-ear headphones iMac as music server (2009) Panamax 5510 w/) ISO transformer LG 65" B6 OLED display