Thank you everyone for your kind words.
akira28, that is a very good question to ask. I am currently using some double sided sticky tape to hold it. But my ultimate plan is to use a little bit of velcro, which should be both sturdy and easily removable. Though I did not have time to look around yet.
Server, I actually found a better sized digitizer at Digikey. It was 5.88" and the transparent window was bigger than the e-ink screen. However, it was out of stock, and was a special order if I remember correctly. So I had to research more, and found this screen as the next best thing.
As for the modification, I would have been a little bit more hesitant if I did not damage the original digitizer. I knew the PRS 700 screen was not as good as PRS 505, but still it looked very good to me. Now, it looks even better
el.astrologo, I would like to do a videotutorial, but currently I am really busy as I am trying to finish my doctorate degree earlier than expected.
I used the excellent disassembly guide by igorsk, and it nicely shows the related screws and brackets to be removed.
The modification is not difficult really, and it only requires soldering on 4 1mm copper strips. I can take some more photos of what to expect there, to help anyone interested.
lilac_jive, to be honest I do not know who to contact, or whether they would be interested at all. I am sure they have their reasons for making the current decisions, and I would be extremely surprised if they did not try these off the shelf screens already...