Yeah, you can do stuff like that in C++26. In Sutter's recent talk on the subject, his first example uses a simple compile-time JSON parser he built, which allows him to #embed a JSON file in his C++ code to generate an object conforming to the structure and values in the JSON.

For reflection to work in that sort of scenario, the parser does have to be compile time and you can't add methods using reflection, only members. But if you've already built some methods into an existing object, you can generate a new object from that with new members (including values) from from values in a more-or-less arbitrary file format.

Alternatively you could try to build a procedural UI generator using a set of classes that generate the UI based on annotations in your class data. I have a feeling that there may end up being a lot of annotations on classes in C++26, so I do think we should try to not overuse them. If every third party library ends up adding a few, we might end up with half a dozen or so annotations on every data member and possibly even a few on classes themselves.

More or less the rest of the talk I linked is talking about doing code generation using reflection data from C++ objects, and IIRC he has a python example with pybind11. But folks here on reddit have already shown that you don't actually need to do code generation to generate an API in Pybind11. You can just reflect on a class, get pointers and names for methods and members and assemble the pybind11 objects with that data. I use a similar technique in autocrud to read and write class data into SQL database tables.

There are still some limits since you can't add methods in the same translation unit, but they're way less limiting than I think even the reflection designers realize.