I am going to address some points about the Pinyin Chinese proposal in this nail that I didn't address in the previous one:

Wikipedia Pinyin Chinese (coded for now as cmn, Mandarin Chinese): Here's a proposal that I think needs some serious discussion. Please read the discussion on the linked Meta page. 

Arguments against:
  • No separate ISO 639-3 language code
  • It is proposed that this can be handled with a script converter, per (for example) T193366.
  • One respondent objected to such a project taking manpower away from other Chinese-language projects.

Arguments supporting:
  • Extremely widely used, and much on-line work in Chinese happens in Pinyin, not in ideographic characters.
  • Proponents state (I cannot confirm) that there are many people who are "illiterate" in Chinese, not having mastered 3000 characters, who can potentially contribute to such a project. If so, that is closer to the ideal of creating projects that "anyone can edit".

I would also note that several other Chinese projects use Romanized Chinese. (All the min-nan projects are exclusively in Romanized language—see Wikipedia here; Min Dong Wikipedia has pages in both scripts.) 

If this project is deemed eligible, I'm pretty sure that it should not be coded with "cmn". (I can let it stay that way in Incubator for now, or give it a q-code.) Test has 250 mainspace pages, and has been active periodically. Last period of substantial activity was during summer 2017. 

I am going to hold back my opinion on this just yet.
* Nowhere in the proposal claims many Chinese online works are recorded in pinyin. What it said is simply that, when one want to type Chinese text into computer, most people would use the "pinyin" system to input those Chinese characters into the computer.
* It is true that there are considerable amount of people in China who are still illiterate. However I don't think many of them can use Pinyin system either. Most of them are illiterate because of they didn't attend schools, which's where the pinyin system was taught. My understanding is that most of them probably can't tell what are characters like "abcd" alphabet are, let alone reading long text in pinyin. Reading/Writing in pinyin correctly would require fluency in the standard version of Mandarin Chinese which I don't think most of those population can do so either.
* "How to let illiterate people involve in Wikipedia" is something that is hard to do. Pretty sure directly letting them to edit Wikipedia would be troublesome as they won't know how to find and read sources and make Wikipedia article that are up to encyclopedic standard. A better way to let them involves is probably to let then be a source via oral history projects like AfroCrowd imitative have attempted and let other Wikipedian to expand articles based on what they said.
* The situation about other Chinese projects that are not Mandarin adopting latin character instead of Ideograph in representation are for inherently different reasons. Those language variants are rarely being written, so in daily life when they do written there are two main ways of doing it. First is to adopt Chinese characters depending on situation and context to see which would fit and write accordingly, and then second would be romanization. In many of these cases, the ideograph representation systems are disorganized and many who use them are influenced by pronunciation of those characters in Mandarin, so it is natural for users to adopt the more systemic latin character presentation, even if it mean greater learning curve to most users, at least there are actually an system that determine how to write them out and books like bibles are actually printed in such character. The situation for Mandarin would be totally different.