Does this include someone who buys BTC on coinbase but never sells it?
If BTC is treated as property (as the IRS says), then no. You'll only owe capital gains tax on it at the point where you sell or exchange it. Your capital gain will be the amount you sold it for minus the amount you bought it for, minus any expenses incurred buying/selling it. (If you sell it for less than you bought it for, you'll have a capital loss.) It's essentially treated like shares of stock.
More details can be found in the IRS guidelines that were linked in the article: https://www.irs.gov/pub/irs-drop/n-14-21.pdf (see questions 1, 6 and 7).