Pretty in line with classical music theory. Further, one would expect that I6/4 chord which was not functionally analysed in the article will be in majority of cases followed by V chord, possibly the two chords sharing the same bass note.
Actually, in popular music I'd expect I6/4 not to resolve normally to V in a lot of cases, since that's a cadence that sounds characteristically old. I'd expect to a lot of I6/4 straight back to tonic (alternating bass line) or deceptively to vi.