Egg crate grids also harden up the light you've softened, the reason it spills is its diffusion which makes it soft, which you are reducing with the grid, so you are going around in circles. The most effective way to maintain softness an reduce spill are cutters.
Panasonic made it clear when they released EVA that it was modular, that they would provide CAD blueprints to 3rd party accessories manufacturers, I seriously doubt that there will be a dedicated Panasonic EVF for the EVA-1. You could of course stump up for the EVF that they make for the Varicam 35 & 35LT, it is excellent and only $5k.
Hmmm, now refresh my memory about the highest ISO on the Ursa?
I learnt the discipline of film in the 80's as an assistant on high end 16mm documentaries and television drama. I recognise the timelessness of film, however, the ability to shoot full frame and super 35 images, with greater iso and lattitude than any 16mm stock, grade them with the same or better result on digital far outweighs the romantic memory of the good old days. Even the use of 2/3 imagers on documentary allows us to capture moments, events and story that was inhibited by beautiful but constrained film. The time has come to move on.
Just interested to know what you do with your 4k output, does it get broadcast or streamed in 4K or are you using it in a 4K projected cinema release?