I'd like the geometry gone as well.
after you have faded them away key visibility (or just visibility)
but that presented some issues to me in the past..
Yes the exporter now needs to work harder, because it couldnt optimize all parts of the work. So you need to disable optimization fo export for it to work if you intend to turn objects back on.
Now the fact that something si in the scene description does NOT need* to mean it uses up rendertime just memory. So unless your running out of memory then i wouldnt optimize this. So unless its specifically a speed isuue then dont work yuour ass of on it, untill it becomes one. The benefits may be minimal in many scenes since they auto optimize scenes better than you can by do by hand many times anyway.
So doing this optimization may in fact slow you down.
But it does make the interactive maya faster true.
*unless you use a pruning material it does use some effort for secondary rays if the objects participate in that kind of stuff.