Rare earths are not rare, the word refers to concentration of the element in the ore, not the prevalence of the ore.
There are many countries that have large reserves, the US included, China has a monopoly because it subsidizes processing, in particular through dumping costs on the environment through little regulation of pollution, not because they are the only country with reserves.
Once we get to scale creation of battery tech enormous amounts of these ingredients will be needed and will be a production differentiator. Good article on harvesting the oceans 'Electric vehicles spur race to mine deep sea riches'
https://www.ft.com/content/00b2e3c8-e2b0-11e8-a6e5-792428919...
There are many countries that have large reserves, the US included, China has a monopoly because it subsidizes processing, in particular through dumping costs on the environment through little regulation of pollution, not because they are the only country with reserves.