Not really. Not because I don't like the nexus, just that I'm not the type who is that much interested in merch. If you can just "sell out" to a different online store where you give them your designs and get a part of the cash, then why not. Might as well try. If you plan on setting up a whole shop on your own, well it will most likely work, because there's a lot of people who love the nexus more than anything, I guess.
In the end, if you don't try, you'll never know if it will work as additonal steady income. Anyway, business doesn't seem to run that bad, so why not try.