Get Block Attributes in JSON REST API

Answering my own question. Since register_meta() actually appends to meta, not blocks, in the JSON output, I just added a new (redundant) attribute to my block using source:meta where I can manually manage outside the attributes I use to display the block.

attributes: {
  api_coordinates: {
    type: 'string',
    source: 'meta',
    meta: 'api_coordinates',
  }, //...
}