Sorry about the delay in replying. Haven't revisited this thread in a while, but inspired by the recent (-ish) release of ZeroW I thought I'd look in again. Also I'm off to a place without electricity in April so phone and MacBook Air won't cut it for computing and I'm back to looking at my Psion Series 5mx and some spare AAs in order to ensure I can still type and work.
Now wondering if the best route to go might be to see how small a package I could fit the ZeroW and a large rechargeable battery into while connecting it to the Psion by RS232–USB connector. Write on the Psion, upload work to the ZeroW & boot up the phone if I need temporary internet. Awful lot of devices to carry, but the Psion remains the only device I have that will offer a decent keyboard and multi-day power in the absence of mains.
I noticed an interesting hack here (but doesn't deal with the matter of power)
http://hackaday.com/2016/07/08/beautifu ... -by-psion/
One of these days somebody is going to get a ZeroW into a series 5 or netbook case.
Oh and there is an attempt to produce a Series 5-like modern PDA here on indiegogo, which seems to have the involvement of the keyboard/hinge designer of the original machine. There are some who are questioning the company, though, as one of their directors was in some way involved in a failed (?) spectrum vega crowdfunding thingie. (I.e. caveat emptor.)
https://www.indiegogo.com/projects/gemi ... vice-phone
If anyone knows of any more progress on all this, please keep us posted.