When the Manual of the Planes came out, and altered the set-up of the planes, with the pervasive astral plane, expanded shadow and cut-back ethereal plane, I thought of an alternative to all that.
How about the ethereal and shadow plane, also be as pervasive across the multiverse as the astral is. Since I'm still using the deep ethereal and like the idea of the deep shadow plane. Have the ethereal, astral and shadow connecting to all other planes. It'll put more significance on the Rule of Three. It works in my idea of a cosmology where the way the planes are arranged are more subjective.
They may exist with other transitive planes, but these three planes would be the most significant.
The border ethereal plane and outer planes may have a somewhat more limited link, in that if you wander a certain distance or stay long enough in an outer planes ethereal, you'll end up in the outer plane itself. Roughly the same would go with the shadow planes borders with other planes. Perhaps the planes themselves pull you in.
Another option would be to use the optional planes from the MotP. Mainly Dream and Spirit, though in some ways I have at least one of them being one of the 5 levels of reality.