and now for something completely different, page-66

I think we need to remember that we're talking about 15% of the periodic table here!
There may well be alternative technologies but rarely direct substitutes.
For example many of the special magnetic properties are due to unique configurations in their INNER electron shells: that's fundamentally an elemental not chemical property.
Similarly phosphors use their elemental spectral properties. A similar spectrum may be built using combinations of other elements and/or chemicals but is unlikely to be anywhere near as 'clean' in colour.
Lastly I'd note that the RE content of an end product is rarely a major component of the cost so if REE are the best and allow the most compact product then they will be the technology of choice once a reliable supply is available at reasonable cost.
NC's sweet spot hopefuly, which I believe is around $50 to $90.