Module support?

There is nothing wrong with what sintakonte has written, he knows what he is doing very well. Let us get away from this "controllers calling controllers" phrase, because it makes people blind. The point is how an independent visual widget (capable to retrieve its own data without main controller's assistance) to be placed inside the main view, or even to be placed inside another visual widget. A library with methods that return HTML output is not the right tool for this purpose. I can tolerate such a manner, not in my projects of course.

WireDesignz' solution conceptually is not wrong. It has a hack inside, but on the other hand, the author had had to stick with the precondition that CodeIgniter's system files should not be touched. On CI4 development this restriction will not be present, so, why not these implementation details ($this, CI, maybe isolation of data inside views too) that are not liked to be addressed and improved, instead of scrapping the whole concept itself and proposing a new one?

There is legacy and practice, I've seen in the past good videos on how CI+HMVC to be used, I think, good links could be found in this forum too. Why would we waste this legacy?

There always be people doing stupid things with HMVC and complaining later. It does not mean that something is wrong with HMVC.

I agree that it is better controllers to be thin, libraries are not the only, the exclusive solution, but this is another topic.