Yes, a very nice and long to achieve.
It will handle unlimited levels and also behind FK's.
Actually it is crazy and passionating.
The result will be showed in a conventional templating, so the custom will not be tricky.
But the SQL construction are bit complex.
In somehow, it will allow any possible level of a sequence composed by FK and XREF mixed up.
N:M are called Xref (Cross-Reference), because it works the same N:1 or N:M, only N:M handle a FK behind.
I want to say it might be available for january or february. I have a lot of details to cure and make a lot of tests.
Keep your breath.
EDIT : Actually, the most difficult part is to modify the javascrip interface, because now the XREF introduces a logic of nested datas and the interface has to be improved. I take this opportunity to improve the framework I have built for this interface. So it might takes more time than 'only' the XREF feature.
It is in a good way, and the memory is handled better (rewrite with more static classes), so it will also improve the speed of loading and bring little bit more comfort.