Did this guy just reinvent spreadsheets? There's something to be said for this, but having written in Prolog, which works that way, the 'reactive programming' people have to make a better case than the article does.
On the other hand, one of the big problems in databases is change notification. Microsoft at one point had a research project on this. The concept was that you could make a request to be notified when something of interest changed in the database. This was expressed as an SQL SELECT statement. When some change was made that would affect the output of your pending SELECT, you'd be notified. The problem was to figure out some efficient way to do this with thousands or millions of pending SELECT statements.
Finance people use notifications like that all the time. Limits on stocks, limits on combinations of stocks, changes in key ratios, that sort of thing. But the systems for that are specialized, a special case of a more general problem. The most general form of the problem is that B wants to know when something has changed at A. Most of the solutions for this have problems. Polling is either inefficient or slow. B relying on A to message them on a change has a failure problem. Both approaches can result in overloading A with checks for events that aren't happening.