The BBC's reporting on it is rather dry and slim, saying little more than "this happened. Here is a brief explanation of what it is and some of the basic reasons why it happened." What isn't really spoken about is what it means, and that's the truly important thing to consider. For one, it distinctly reminded me of George Friedman's The Next 100 Years, in which he forecasts the Third World War to start in 2050 with attacks by unmanned hypersonic aircraft against the United States, Poland, and the rest of its coalition. The way I see it, hypersonic missiles are poised to reinvent the idea of warfare similar to the way intercontinental ballistic missiles did in the mid-20th century, and destabilize the 21st century political environment.
What really concerns me is how the United States will act when it has a hypersonic monopoly. It would have the ability to strike anyone, anywhere, with practically no warning at all, and whether or not an ability is used has little bearing on how that will be perceived elsewhere. I would imagine that once the United States starts building a hypersonic arsenal, everyone who is not already a staunch US ally will feel more threatened, and be justified in doing so. Missiles that fast can't be intercepted by aircraft, and it would take an extremely lucky shot for anti-aircraft defenses to knock one down. In many, many circumstances, hypersonic missiles would give the United States to strike anywhere it wants with utter impunity.
The Phalanx Close-In Weapon System aboard HMCS Algonquin. With an effective range of two kilometers, it'd have approximately one and one-quarter seconds to shoot down a hypersonic missile moving at Mach 5 before impact.
Sure, to a degree the United States already has this ability; but that's only to a degree. While its bombers can reach anywhere on Earth, a significant chunk of the modern American bomber force is subsonic. Aside from that, there are psychological factors at play: bombers are known, bombers are familiar - and bombers can be shot down. Even stealth aircraft can be shot down, as the Serbs proved back in 1999 when they shot down an F-117 during the NATO bombing campaign. That the United States has the capacity to send a bomber anywhere and drop some bunker-busters if it feels that it needs to doesn't really generate friction on its own.
Hypersonic missiles are a different story. Basically, unless you already operate a ballistic missile defense system, you're not stopping a hypermissile. Sure, you might be able to see it coming, you might be able to get out of its way, but nothing more than that.
Granted, I don't believe - at this point, at least - that the United States really would start using hypermissiles hither and yon outside of extremely unusual circumstances. The point, however, is not what it would do; the point is what it could do, and how that it is perceived by its rivals. It's easy to imagine how states that aren't on the best terms with Washington might see a hypermissile force as an existential threat. The way the reactions to such perceived threats manifest may greatly influence the geopolitical landscape as the century drags on.