Is there any !28GB internal memory variant out there?

I can't remember seeing any indication of there being any multiple versions of the Action 2 based on the memory capacity. Releasing those could have some possible commercial potential, provided they can also alleviate the overheating issues some have experienced.

https://store.dji.com/hu/product/dji-action-2-128g?vid=162651

Hi there. Thank you for reaching out. We highly recommend using a recommended SD card for your DJI Action 2. You may check the image below. Please don't hesitate to reach us if you have other inquiries. Have a nice day ahead!

What's then the purpose of having 4x embedded storage?

more starage in the camera, cheaper and better than insta go3 128gb