This really needs to be implemented. I use a lot of Twixtor Pro in my sequences, and the filter often requires that you nest the source clip in a nested timeline and paste repeated instances of it to ensure that the plugin has enough media to work with. You then apply Twixtor to the nest itself. But you cannot utilize Render and Replace in these cases, which really frustrating, because this is a prime example of a situation when you'd want to be able to use such a feature.
A nested timeline should be considered a "clip" in this context.
It's weird that it doesn't, since the render and replace function presumably exists for effects heavy situations where you need playback optimised and those are exactly the scenarios you're most likely to use nests.