Any claim of the form "this language is magical! every statement is self-evident" has been bunk since the dawn of programming. The people making such claims are always already too close to the language to realise their own confirmation bias.

So, feedback, from someone whose exposure to Swift consists basically of this article but has eaten a metric crapload of many other braced languages over the decades.

What I can tell is that the programmer wanted to print 2,4,6,8. So the intentional readability is there. However when it comes to understanding how it works (i.e. the language mechanics delivering the intuitive reading) I had lexical concerns. I couldn't immediately tell whether the where-clause acts like a guard predicate in the for-statement or an unbraced if-statement i.e. equivalent to

    for i in 1..<10 {
        next if !(i % 2 == 0)
        print(i)
    }

or

    for i in 1..<10 { 
        if (i % 2 == 0) {
            print(i)
        }
    }

or even (let's hope not)

    if (i % 2 == 0) {
        for i in 1..<10 { 
            print(i)
        }
    }

and in a similar vein the lexical scope and binding of i was not clear to me; some languages bind the iterated variable at the level of the statement, others inside the iterated body (which may even be a closure for all I know), and this has implications particularly for the the value of i after the loop, for the binding of i in any function generated inside the loop (example: print could actually talking to an IO object that defers output by prepending lambdas to a chain - I've seen web containers deferring view rendering this way), for name masking, and for the consequences of any flow-control/continuation/exception mechanism that may cause an early loop exit.