I can't tell you how they've implemented it, but OpenBazaar has a Onion transport implementation of IPFS that seems to work. It's not as simple as "glue Tor to the IPFS port and hit go", of course.

TCP DHTs may not be efficient, but efficiency isn't one of IPFS's strengths anyway, in my experience.

Private IPFS networks for each Quiet community make this not a problem. I haven't investigated using Tor on the big global IPFS DHT, but we don't have to worry about that.