I came across “Critic markup” a bit ago and it looks interesting. Kind of like file diffs on GitHub, etc. It might give you some ideas.
Critic markup altered a bit to not trigger ==highlights or ~~strikethroughs in Obsidian:
Addition {++ ++}
Deletion {-- --}
Substitution {~ ~> ~}
Comment {>> <<}
Highlight {= =}{>> <<}
Even if not the critic markup syntax, you could use a plugin like wrap with shortcuts to set hotkeys for whatever syntax you decide on using.
Using variations of these would be easily searchable using regex or just plain search strings.
Sounds fun. I’m interested to see where you go with this. 