[Feature Request] Allow custom meta value control extensibility

[Simbaclaws]

Hi there,

I think it would be a nice addition to have the flexibility to extend the custom meta values that can be used within the meta queries with custom controls.

This way if someone for example has a date meta field that they use on their custom post type. A developer can add controls that can help query this custom post type on the custom meta field based on for example the current day, or next week, or whatever have you.

Suppose you have a lot of different meta fields with different types of data and you want to query them in different ways, it would be nice to allow a developer to extend on top of that functionality to let them build whatever they want to.

Maybe some sort of hook could work, or a variant of the advanced query loop block?

Please let me know what you think of this idea.