I don't doubt that using org outside Emacs may be problematic to some degree (in terms of expected functionalities, anyway), but I use Emacs for everything, so

I don't doubt that using org outside Emacs may be problematic to some degree (in terms of expected functionalities, anyway), but I use Emacs for everything, so it's not really an issue. If popularity alone were sufficient for technological choices, we wouldn't even be having this discussion (and we'd all be using Windows). I try to choose my tools according to how well they work for me. Markdown, in my opinion, is a poor choice compared to org, but I can use it to collaborate with others, no problem. As for the transition from light markup to TeX, that's pretty much the point of the OP, isn't it? Maybe the break point is different for everybody. For me, LaTeX imposes no extra cognitive load, but then again, I've been using it extensively for many years. If I'm need for something lighter, it'll be org (but really, org usually wins for me because of how well it does all the other stuff, not just the markup part).