Quite the opposite. They do have a scalable and profitable business today.
The biggest component of their operating cost is Sales & Marketing. The Sales organization was the main cause for the costs increase in 2014, but it won't continue to grow linearly with revenue for much longer. Maybe a couple of years more, as they ramp up sales teams outside the US, and then it'll flatten out.
On the other hand, the cost of Marketing is not really marketing. It's infrastructure + customer support for the free users. For now it's an investment, and they are hoping to monetize by converting into paying customers, or some indirect way in the future (e.g., advertising).
Let's do a quick thought experiment. Turn it off its free users, and focus only on the 34K paying companies. Plus, to keep existing paying customers you don't need an army of 600+ salesmen, so you could get rid of them too. What is left is a company that is extremely profitable and cashflow positive, with a nice and sustainable business.
Naturally pre-IPO companies are better-off by focusing on exponential growth, instead of profitability. The enterprise cloud storage market is a gold rush. Dropbox, Box, Amazon, Google, Microsoft and EMC all fighting for the same corporate dollars, so there's no time to waste.
The next couple of years are pretty clear for Box and Dropbox. I think the interesting challenge will be in 2-3 years, with the upcoming commoditization of this market. When everyone has a Storage-as-a-Service product, and their apps and web interfaces became good enough, how to you convince IT folks to justify tens of thousands of dollars per year?