The Channing iterations all used a passerelle, albeit a narrower one than is seen at the Shubert. It circled the orchestra, but probably was not as safe. The current version really looks like an apron with a slit in the downstage floor to see the orchestra. The old one was a ramp-like structure that encased the opening. I suspect it's possible to built out over most orchestra pits. I may be wrong.
Did anyone see Channing in a "Dolly" tour without it? I saw it at the National in DC back in the day (first with Bailey, en route to B'way, then with Channing in the mid-70s). It had a version of this feature.
"I'm a comedian, but in my spare time, things bother me." Garry Shandling