I wonder if all the projects using "bitcoin" as part of their name should somehow report and pay to the copyright holders, as it's rather misleading
Not necessary as far as I know part only of the name of company or product is only included not the exact word is copied is not a copyright violation bitcoinus is different from bitcoin so there is nothing to worry from the side of developers correct me if Im wrong.
I can't think of a way to hold someone liable to put the name Bitcoin into a project or product name. Unless it is a registered company from the stock market, but in terms of copyright I doubt it that there is anything you can do about it. Also, who is the copyright holder in terms of Bitcoin? Do you know them?