I'm curious too- I like making lithophanes (just started, but like it!!) as well as cutting some plywood parts... and blue foam...
A 4x4 interests me as the extra working area would allow me to set-up fixtures in various places on the table and then leave them there. One corner makes lithophanes, the other side takes pieces of foam, and so on.
We've seen videos of the latest (and greatest!) 4x4 machine plowing plywood at bit-snapping speeds. How about doing 800 lines at .009 step over per line?