Thousands of people have made it down the path to nationality in Honk Kong. Acquiring Chinese nationality -- whether mainland or not -- is possible. It's just that the standards are very, very, very exclusive.
On paper, there is also path by which you can marry into Chinese citizenship, but it's exceptionally rare in practice.
"Renounce other citizenships" is complex. Many nations don't provide a citizens with a means to stop being citizen. Which is to say, if you take a Chinese (or any other) citizenship, and renounce your old citizenship, you may still end up with both citizenships.
I don't know specifics about Honk Kong, but I do know the standards are laxer than mainland China.