Iframes have always been "bad", ever since they were introduced by IE in the late 90s (?). Inconsistent browser support, weird janky way of existing in a page, having their own scrollbars, not being able to stretch to fit their content or move when pushed by adjacent content, were iframe issues that I remember being very apparent in that era.

but perhaps these issues have all been remedied? And Iframe is now the perfect container for a modern day component?

... passing messages directly between parts of a page distinctly unfashionable in the age of redux and context. Having each component be its own request to the server - bizarre-seeming in 2021 but maybe something transformational there if our future is moving back to server-rendered HTML ... some crazy blockchain webserver coordinating ui state across dozens of tiny frames in a webpage, each with its own crypto account ? ... could be great, who knows

[edit: if I have just engaged in debate with an AI programmed to generate absurdities (per @solarpunk's comment), I have some preconceptions I'll have to go and reevaluate now]