Is this idea doable? How hard would it be to implement? Reference discussion.
It would be great if we could hook in, say, [[link]]s and then write on-hover preview of the linked page in Lua or do other insane things like that. 
Sidenote: For me it would be great if I could do what’s mentioned in the referenced discussion: to make hook in $ ... $'s AST node to use @MrMugame’s ${latex.inline(...)} and similarly to hook in $$ ... $$'s AST node for the ${latex.block(...)}.