Hebrews 2:1-4: A Propositio?

Michael Bird has an interesting question at the Euangelion blog concerning whether Hebrews has a propositio (similar to a thesis statement). Bird writes,

Does Hebrews have a propositio? (Actually, does any NT doc have a propositio, but that is another matter). Recently, Ben Witherington has argued that since Hebrews is a piece of epideictic rhetoric it has no propositio. But if I had to press one passage that certain does fit the function or role of a propositio in Hebrews, it would have to be Heb. 2.1-4:

My knee-jerk response was "no." I have always understood 2:1-4 as simply a warning passage but I must admit I am now thinking about Bird's question. Make sure to read his entire post here.