I have seen no rumors to that effect. It has been awhile since the latest 10th generation Kindle shipped, however, I think the longest between generations we have seen.
E-Ink does have a slightly improved panel (has the touch layer integrated and they claim 30% increase in contrast ratio for B&W and 40% for color, with 15% improved saturation). It is certainly reasonable that Amazon is working on devices using these.
https://www.eink.com/news.html?type=...ar=2021&page=1