The report echoes a well-known joke/prank wherein people discuss the dangers of the chemical "dihydrogen monoxide" also known as hydrogen oxide and hydrogen hydroxide. Search online for information about dihydrogen monoxide, and you'll find a long list of scary-sounding and absolutely true warnings about it: the nuclear power industry uses enormous quantities of it every year. Dihydrogen monoxide is used in the production of many highly toxic pesticides, and chemical weapons banned by the Geneva Conventions. Dihydrogen monoxide is found in all tumors removed from cancer patients, and is guaranteed fatal to humans in large quantities and even small quantities can kill you, if it enters your respiratory system. In 2006, in Louisville, Kentucky, David Karem, executive director of the Waterfront Development Corporation, a public body that operates Waterfront Park, wished to deter bathers from using a large public fountain. "Counting on a lack of understanding about water's chemical makeup," he arranged for signs reading: "DANGER! – WATER CONTAINS HIGH LEVELS OF HYDROGEN – KEEP OUT" to be posted on the fountain at public expense.
I do have the development branch of kdeconnect installed, which I THINK is the kf5 port - it seems to work fine.
They've split the core system and applications development, so I assume that as KF5-native apps are released, they'll just replace the kf4 versions. I'm assuming most distributions will consider them "testing" or "unstable" versions for a while so you'd have to explicitly ask for them (for the first few versions) instead of having them just pop up without warning.
With the core libraries that they depend on in apparently pretty solid shape as of KF5.6 in my experience, I suspect the kf5-native applications will stabilize pretty quickly once they come out.
KDE4's apps still work under it, too. I'm using it fine, though I'm missing the "IM Presence" widget for kde-telepathy.
I actually haven't been seeing crashes or other serious problems so far since about the last couple of releeases (KF5.4), just missing "KF5-native" features from KDE4.
My dog wouldn't eat sea cucumber.