Wikipedia has an article on the 7/6 chord. It only shows chords built on major triads with added major sixth and minor seventh intervals. For example, a C7/6 chord is comprised of C E G A B♭.
How far is this notation taken? Consider these possibilities:
Cm7/6 - C E♭ G A B♭
Cmaj7/6 - C E G A B
Cmmaj7/6 - C E♭ G A B
C+7/6 - C E G♯ A B♭
C+maj7/6 - C E G♯ A B
Cø7/6 - C E♭ G♭ A B♭
These can certainly be parsed without ambiguity, but are they better-written (or written in a more standard fashion) as Cm7(add6), Cmaj7(add6) and so forth?