Like Crooketarrow, said, it would be ok for an emergency situation, but the bow would have to be low weight, I would think, and yes wrap the nock, and point notch well. Like C A also said, there must be some shoots around you. The winter is the best time to look, as the leaves, are off most of them, and you can get a good look at them. Also, tomato stakes, (bamboo), dowels, Spruce, Fir, etc. 2 X 4's, cut down to size, I think 3/4 by 3/4 square, and just keep planing off the corners, till you have a mostly round shaft, then just sand till it is round, and smooth and then straighten, and seal.
Then try to match the weight of the shafts, and spine weight as close as you can.
But I would think Cattail shafts would not be worth the trouble, unless it was a quick need, and then I doubt it would hold up to much shooting, especially from a bow above 40lbs. or so. Even if that. But would suffice for survival for rabbits, and such. Just my own humble opinion. I could be wrong. And that would not be the first for me.
But do try it, and let us know how they turn out. But be sure to wrap at least an inch or so from the nock notch, and the same from the point notch.
Wayne