Please give more insights about what a possible implementation would look like and more importantly what benefits it would bring.

IIUC Marshaller is just a serializer but another name was chosen not to create second SerializerInterface class in Symfony ecosystem. JSON string is a type of serializer string so one may want to store the cached value as a json (e.g. cache as json and return cached jsonstring directly from API). Integration with Serializer Component would allow that.

Take a look: https://github.com/symfony/symfony/tree/7.2/src/Symfony/Component/Cache/Marshaller

Thank you for this suggestion.
There has not been a lot of activity here for a while. Would you still like to see this feature?
Every feature is developed by the community.
Perhaps someone would like to try?
You can read how to contribute to get started.

Could I get a reply or should I close this?

Hey,

I didn't hear anything so I'm going to close it. Feel free to comment if this is still relevant, I can always reopen!