What will they replace? Certainly a lot of CRUD programming. That's the absolute sweet spot for now. But make no mistake, high performant enterprise-grade systems with 10.000s of concurrent users are also being built.
I personally don't think it's the visual programming that makes the difference. Instead, the magic is: the very tight integration between forms, logic and data model. This allows rapid application development (not prototyping!) of web/mobile applications. Hardcore developers become many times more efficient and "citizen developers" can still contribute things such as business logic without knowing all the low-level details. All the boilerplate BS of modern web apps? Gone. Instead you just have an IDE with a "Run" button.
An example: remove an attribute from an entity in the data model? On next deployment, the system will remove the column from the database automatically. Also, the IDE will show errors (within a second) in all the forms where the attribute is still being used, so you know what to change. This gets you in a state of flow very quickly. I know many developers that would hate switching back to Java/.NET because they can't get nearly as much done.
The tight integration is possible because the syntax of visual programming is simpler/more limited (and very strongly typed). This allows the compiler/IDE to reason about what the "code" is doing.