I also believe an iPad is a useful compromise today. If you really want an ideal device, I don't think twelve inch eink using today's tech will be worth it.
First let me explain the earlier comment about a flexible backplane. The issue is that a thin eink screen is likely to break in a large screen format. Flexibility is to help it withstand breaking. In addition, I imagine the ideal screen would fold or roll for transport.
Second, academic writing really calls for interactive features for highlighting and note taking. Eink is still best for static/unmoving displays. To be able to smoothly annotate you would prefer a touch screen interface with a display that can smoothly refresh.
It probably also needs basic multitasking so you can copy/paste or otherwise extract your notes and content to either email or a word-like document. This latter comment doesnt relate directly to the eink display, but to a characteristic needed if you decide to design and build such a device
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The bottom line is that I think your intent makes sense, but that the ideal tech just isn't ready. For me, the best compromise today is an iPad with iannotate software. In horizontal mode it displays a full page width. Although the page is cut in half, the fact that you can smoothly drag the page to scan it and pinch to zoom out offsets the page size problem. Of course these features aren't really possible with eink today given its relatively slow refresh rate.