In my experience pandoc is not better than TeXmacs in converting LaTeX. The problem, as vdhoeven stressed, is that LaTeX is not a document format which can be converted reliably in something else. Usually I just convert to LaTeX the last version of the document, e.g. before submitting to journal. In this way I always dispose of some alternative storage formats: TeXmacs, PDF, LaTeX and sometimes HTML if needed. The LaTeX produced by TeXmacs uses few packages, which also means that it can be easily maintained.