What's the problem with nodes supporting or not some properties? For querying you can treat all nodes as supporting all things, and the user just needs to write

What's the problem with nodes supporting or not some properties? For querying you can treat all nodes as supporting all things, and the user just needs to write a query that acutually works, which is what they would need to do anyway. Yes, if you want to make the query language reject as incorrect queries that specify a property on a node that can't have properties, it is messy. But is this really necessary? You can write faulty queries anyway. And it's not a programming language for complex systems, where it really helps to prevent mistakes early. SQL works fine with no type safety and so on.