The main problem I can see with that sort of system is that it probably would get quite unwieldy for decently complex chord patterns (try scoring a chord pattern up the keyboard, say, like what's at the beginning of Tchaikovsky's Piano Concerto 1 for a start -- http://imslp.org/wiki/File:PMLP02744-Tchaikovsky-Op23v1FSmuz...).

For other styles I think it would be pretty good; although the score won't be as compact, it might be easier to understand a "fake book" scored piece (ala what's used a lot in jazz) written this way, let alone pop (which often can be represented with a melody line and Roman numeral chords).