I know this is not the right place to suggest new feature but have a look at Wordpress’ Pods plugin. I would love to see this in core of Modx. This plugin creates custom post types ( CMPs ) and also give option to include it in rest api, show on menu, user roles etc. I dont know why its so hard to make this in Modx. This can easily be part of Modx core. Why I am saying this because world is moving to js frameworks like react and vue and what they want is Rest Api. So creating CMPs and Rest Api with custom fields (tvs to n db table) would be great to kick start a new static website with rest api for mobile apps.
Please have a look on this plugin. I am using it for many of my sites and this is the most wanted thing I love to see in Modx.
PLEASE TAKE MY WORDS SERIOUSLY AND HAVE A DEEP LOOK ON THIS.