Customization entry point on GetCartResult sub DTO's

Hello, Recently we had to add a custom property to the ShipVias, and making that new property available on the updateCart API was very inneficient.

If we look at the GetCartResult class, there's a lot of sub dto's used that are not extensible without a big amount of customization. To add a property to the ShipVia DTO, we would need to have a custom GetCartResult, Custom CarrierDto, Custom ShipViaDto, and refactor all existing handlers that used the original versions to use the customized versions instead. This is an insane amount of work, and an issue in terms of maintainability.

What I propose is to have all DTO's descend from a shared class that contains a property dictionary, similar to what it's done with the Result, but also for the inner DTOs.
If this was the case, the entire customization would be one handler, adding the custom property to the property dictionary. That's it.

I came across this issue for this particular example, but I'm sure it's probably applicable to more places than just this one.