Initial default key/value pairs would be great in order to keep a feature properties organized. Also, an option to prevent from creating new ones beyond those initially set, would allow greater control on many specific use cases.
After creating my own features (polygons, points) on Mapbox Studio, I've set custom properties for each feature such as follows:
"properties": {
    "name": "Place Name",
    "type": "neighborhood",
    "deliveryFee": 3,
    "city": "City Name",
    "active": 1
}
 
I've developed a MERN Stack app where all the features area now stored on mongodb... I'm able to CRUD and filter features by properties in many ways through a REST API, so in order to keep those properties standard, I'd need to lock a feature properties as mentioned.