For example,
when I type [[apple|apples]] in one note, and [[apple|favorite fruit]] in another note, I would love for it to auto-populate the [[apple]] page with:
---
aliases: apples, favorite fruit
---
This is so that in future, when I want to create a link, it is automatic.
Anyone else who also thinks this is really good?
One way this could be implemented can also be a dropdown menu that pops out whenever we try to create an alias for a link. with “Insert alias into page”.
Nice idea!
I also find this a very great idea! For some people using Obsidian in different languages it could greatly reduce friction. Feature requests and plugin ideas have been posted since Nov. 2020:
Add aliases to frontmatter by right click on a link with alias
Automatic update aliases metadata
Aliases, Inflection and Auto-Updating
Maybe we could get some traction for somebody to be interested in making this work 
There is a plugin that does this: see the post New plugin: Link with alias - Fast link creation including link alias - Share & showcase - Obsidian Forum. You might have to tweak the options a bit to get it working right, but it’s been working for me to do exactly this.