True Left

"Native American languages like Guarani"

These should certainly be taught as part of a decolonized Classics curriculum in American schools, similar to how Latin and ancient Greek are taught as part of the Classics curriculum in British etc. schools:

https://en.wikipedia.org/wiki/Classics

While Latin is no longer used for daily correspondence in Britain, it is the default for ceremonial text:

https://c8.alamy.com/comp/2FA4YFK/coat-of-arms-and-latin-inscription-on-old-school-building-harwich-essex-england-uk-2FA4YFK.jpg

This is the role that I can easily imagine Guarani taking in Paraguay, and so on, and something that the state could implement with relative ease. If it spontaneously grows to become the default for daily use too, then great! But the state should avoid trying too hard with the latter.

"I also feel like it's more expedient for Latin America to stick to exclusively Spanish"

For daily use this would be more convenient in the short-term. The regional Counterculture era also used Spanish:

https://www.youtube.com/watch?v=2k70mf5ZDDw

so discontinuing Spanish would mean cutting people off from such works, which is not my intention.