I've just read the article, it's relatively interesting. Without commenting on his general conclusions, which may or may not be right, I would point out that he's a bit of an idiot when it comes to being prepared. [Edit: Actually the author is a Michelle Arthurs-Brennan, so "she" not "he".]
He had valves that needed a tool to remove them (pliers or maybe another tool) and he didn't have the tool. Had he not given this any thought at all? Had he not at least mentally rehearsed the procedure for inserting a tube and checked that he had the tools? Evidently not. He was riding tubless tyres without carrying plugs - but in retrospect he's decided that they probably wouldn't have worked anyway.
That's a bit like complaining that tyres in general are a terrible idea because they require tyre levers to remove them easily. And who on earth carries those? Or riding a bike with wheelnuts and saying "I have no intention of ever carrying a spanner". I really have no sympathy for him. He seems to expect problems to magically sort themselves out without the right tools.
He may be right, but that doesn't mean he's not an idiot.
Full disclosure: Yes I use tubless tyres. Yes I know how to remove my valves and I carry an appropriate tool. Yes I carry plugs. Yes I carry tyre levers and a spare tube. No, I don't know if plugs will work as I've never needed them. I'll wait until I have a bit more experience with them until I settle on an opinion and start shouting at people about it.
As to the bike shop owner who says "I've tried a host of modern tubeless road tyres and I only ever get 400 miles out of the rear tyre before the tyre slashes and the sealant won't seal." I have well over 1,000 miles on my new tubleless. No puncture incidents yet, or at least one that I know of. Maybe I've just been lucky and will live to rue my words, who knows?
The bike shop bloke adds: "If I'm asking my customers to spend £60 on a tyre and they can't get more than 400 miles out of them, I feel like I'm taking the p*** out of my customers. If they put a tube in, they get 2,000 miles out of them before it's worn out." 2,000 miles?? What kind of tyres is he selling to his customers that are worn out after only 2,000 miles, tube or no tube? I'm not going to that shop.
The article concludes: "And please, if we could come up with some sort of rim and tyre compatibility code ... that would be nice too." Well, at least I agree with that.