You are commenting, yes, but "to riff on something" usually implies that one is commenting in a comedic way. The phrase actually comes from jazz music, where there is often a solo feature of a player (e.g., saxophone). If you are familiar with jazz, you will understand that these solos are often improvised--they don't follow the sheet music and make stuff up. These are called riffs. While jazz isn't funny, the phrase has been extrapolated to be used in everyday conversations. Someone who is "riffing on something" is improvising and going off script, commenting on a topic usually in a funny way. I'm not sure why it implies something humorous, but that's how the phrase is used today.
A famous American actor who did this often was Robin Williams. If you ever watch an interview with him, he is easily able to switch from serious to funny. And while being funny, he sometimes was able to riff on some serious topics. Another person that comes to mind is British comedian, John Oliver. He has a series on YouTube called "Tonight with John Oliver," in which he presents news in a comedic way. He is a great example of "riffing on ____." While John Oliver's episodes are 20 minutes in length, he manages to riff on a lot of different topics.
Now for your original statement, I could see an expert comedian "riffing on" the housing crisis. For most of us, however, it would be difficult to pull this off because we might offend someone. By saying, "I will riff on the housing crisis," you're saying that you'll make a joke of the housing crisis.