Thanks. DH Box looks like it can help make things a bit more efficient. The FX Plug-ins are more for transitions.
I guess the FCP architecture itself does not lend itself to “one-click” implementation of common ‘scrolling and pushing’ split screen effects, that are used in documentaries and commercials. Using the motion controls, key frames, opacity settings with multiple video tracks (or using Apple Motion) seems to be the workflow.
Maybe one day someone will come up with a workaround that makes such editing tricks as easy to implement as a blur filter.