Profitable compared to electrical usage is the only viable thing, really.
You don't have to shut down BTC/etc. mining for it, after all.
Also keep in mind that TBX can be mined effectively on regular everyday hardware, no special GPU requirements, which means that a lot of folks with free electricity just got the ability to mine. I for one would like a Java/JavaScript miner so that I can dedicate a core or two in the background while I'm at work.