It’s not needed right now, i agree. Before going to graphics full moddable engine may be prepared.
By the way, i had a throught that scaling of PNG images is good to be suported as option.
Something like
"images" :
    {
        // Group of this image. Optional, default = 0
        "group" : 0,
        // Imdex of the image in group
        "frame" : 0,
        // Filename for this frame
        "file" : "filename.png",
        "scaleX": 50, //percents - 100% if not set
        "scaleY": 50 //percents - 100% if not set
    }.
    ...
]