It's not about this causing issues IMO. It's just.. why? Why would '+' not be commutative? Why not throw an error? What is the use-case for "adding" '[]' and '{}'?
Or, put another way: why would a programmer want to have this "feature" instead of being notified: "hey, you're adding '[]' and '{}', that doesn't make any sense, fix that!"
Sure you can work with a language like that. But it sure doesn't feel like somebody thought all of this this through.
No, Vim plugins wouldn't work anymore. Vimscript will be transpiled to Lua under the hood, though, and other languages will be fully supported for writing plugins.
Or, put another way: why would a programmer want to have this "feature" instead of being notified: "hey, you're adding '[]' and '{}', that doesn't make any sense, fix that!"
Sure you can work with a language like that. But it sure doesn't feel like somebody thought all of this this through.