I don't think it can be classified as "resolved". It's a good way to show optional arguments (which I appreciate), but there is a lot missing from the "solution".
\refstepcounter{subsubsubsection} to step the counter?
\addtocontents{toc}{#1} to add the table of contents?
hanging numbering?
\newcommand\thesubsubsubsection{\thesubsubsection.\@arabic\c@subsubsubsection} to define the referencing?
It's just odd that you can take the same definition for the subsection, change "subsection" to "subsubsubsection" and all of a sudden it repeats.
You can use titleclass out of the titlesec package, but I've noticed that it jacks up the table of contents and I don't know how to fix it...got another thread going on that one.