Honestly, 13" is more than you need for a 4:3 terminal. A lot of classic character terminals had 9 or 10 inch screens...it's not until you get to like the VT320 that you have a 14" screen. I'd consider a 10 inch screen about ideal, and the keyboard doesn't have to be 13", either.
We are making prototypes in 3 different 4:3 sizes--10.3, 12.1, and 13.3. 13.3 is furthest along. The end of your comment talks about the real size restriction for us--keyboard. We do not want to compromise the typing experience.
Around 12" (in a 4:3 body) is about as low as you can go without messing with the typing experience much. The problem at that size is the available e-ink panels are S-L-O-W; no fast refresh models are out there.
(You might ask why we would even do the 10.3" prototype if we know that's too small for keyboard reasons? It's mostly for marketing reasons when we actually try to try to get attention for this project. The 10.3 is going to use a Thinkpad 701c butterfly keyboard in a custom body just for the "wow!" factor in showing the sorts of things that are possible. The 10.3 would actually be a killer end-product, but no similar keyboard is in current production so we couldn't actually make it).
