[mLuby]

Anyone know how the unusual consonant x was chosen to replace a and o rather than another vowel (like e)?

To my untrained ear, les neen-yes sounds more in line with los neen-yos and las neen-yes than lecks neen-yecks (if that's how you'd pronounce it).

[lodi]

It's just 'x' as in the mathematical variable 'x' for something unknown, e.g. suppose a train is traveling at 'x' km/h... They use "latinx" to abstract over "latino/latina". Of course this makes zero actual sense in Spanish.

[deviantfero]

Because Spanish speaking people did not come up with the concept and people that came up with the concept were maybe not that familiar with spanish pronunciation or weren't concerned about it at all, I've heard that this originated strangely enough in Portugal but was made popular by some people in the US, I might be wrong on that one though.

[pseudalopex]

Bilingual LGBTQ people used it before it became mainstream English.

[bnjms]

It likely came about in written form then was moved to speech.

I’m in agreement with you that é is the natural neutral replacement letter. But I don’t think this is a serious attempt to change the language so much as a serious attempt to signal group membership.

[pseudalopex]

Latinx came from LGBTQ Hispanic people. It was influenced by spellings like folx and womxn probably.

It became popular in writing first too.

Some people do say Latine. Probably it will replace Latinx eventually.