Perl objects worked like this and the ecosystem is a mess as a result. There's a built in `bless` to add a vtable. There's some cool stuff you can do with that like blessing arrays to do array of structs vs struct of arrays and making it look like a regular object in user code. The problem is there are like 4 popular object libraries that provide base stuff like inheritance, meta objects, getters/setters etc and they're not all compatible and they have subtle tradeoffs that get magnified when you have to pull multiple in to get serious work done.
Let me ask this: hypothetically if they wanted to, would it be possible for Zig to add a language feature called Interface which provided to the user "...an easy way of creating one".