sitting in university, I often image to be capable of adding Latex equations to my pdfs. I imagine it this was to be implemented:
There should be a second text environement specially for latex. The latex code intered there will be wrapped into a latex document, compiled external with the latex distribution, then rendered to a transparent png and inserted into the xournal layer. And the latex code should be stored seperatly, so that you can change the formula later. There are already skripts out there, which render latex formulas to png. This should be just possible more comfortable from within xournal.