Is the pi zero usable speed-wise? 

I've got one running raspbian and idled (https://obsolescence.wixsite.com/obsolescence/pidp-11-how-to-use) in my PiDP-11 and just ssh'ing to it takes upwards of 20 seconds.

Very impressive. Great build. 

I have a 200LX catching dust and have played
with the same idea but could not figure out
to keep the keyboard going. Any pointers you 
can give on how to make the mapping not so
painful? How did you solve the powering down? 
Do you have some source info on the parts used
(E.g. LCD, adapters, etc.)
Will you do a full write up? 

to answer your last question first..   

I may....  do a bit more of a write up.  but its not likely to be exhaustive, is fairly involved to fit all the hardware, case modifications etc..   its the Journey right? ;)

i will probably post some details, specific to the keyboard and on driving the higher resolution LCD directly DPI. 

KEYBOARD. 

your first challenge is really the "hardware"
how you are going to connect to the flatflex?

then i used an Arduino MEGA. (you need the high pin count),
and a sketch i found somewhere to scan the keyboard matrix..   
then its "just" down to pushing buttons and modify the standard
Teensy USB keyboard sketch to match. 

and of course, as the HP95LX does not have the regular layout.
i had to remap a lot of buttons within Linux. 
all those custom amber and green chars etc...
(i did a-lot "dirty" tricks to make it work and I'm entirely sure there are neater ways)

HARDWARE
i used mostly off the shelf (as small footprint as possible)
Ebay "China" devices,  USB-RS232,  USB-Ethernet, USB audio, USB hub etc.  

LCD   
the "usual suspect" 4.3" LCD  has got a 480x272 resolution. 
which works.  but is pretty poor.   i managed to find my one on Alibaba. 
but you will have to contact a lot of sellers to get quantity of one.
you need a 40pin LCD breakout  and back-light boost circuit of sorts too.

othermod raspberry pi LCD topper comes to mind.

Power down.. 
I didn't have success with the raspberry Pi. powering up and down. "soft" 
so its a sliding power switch on the back for now. 
i considered using the PCMCIA eject slider mechanism as the power button. 
maybe later

the keyboard power button is mapped separately. so an external circuit should be possible. 

I appreciate your candid response. I do hope you write some more regarding your great build. 

Do you have a few part information of what you purchased. Especially regarding your display and power management. 

I opened my 200LX over the weekend and had a look at how you put this all in there. I’m amazed that you got it all in there. 

Hope to read more from you soon.

Maybe a bit late but it can help others.

Concerning the keyboard, this project can be of some interest

https://hackaday.io/project/162281-teensy-thumb-keyboard

Very nice work! That keyboard with its tiny numpad looks really useful for when you inevitably end up using this as a calculator. Are you satisfied with the screen resolution? Is there anything else you would do differently if you built the project again?

I used to use this very same HP95LX back in say 2000's  with MS DOS on it.
and the keyboard and number pad is very usable indeed.
at-least for the Palmtop sized "fully fledged" linux termial device.  

I personally use Midnight Commander for alot of basic stuff.
so Critically for me. it has got a the F1-F10 keys. aswell as just about any symbol i can imagine printed on it.

A Psion 5 device for instance.  (which i would love to do next.)  has a great mechanical keyboard, and formfactor. but its limited for Linux use i think.

as for the screen. I managed to source this 4.3" 800X480 screen. 
(not the usual 480x272  you see everywhere else) 
(this LCD has about 3x the pixels of that)
and with this resolution, for the CLI i even increased font size,  as the text it got a bit on the small side.  so overall for the size of the display. PPI is actually quite good.   

if you want higher resolution even. then I have been looking at both LCD and AMOLED displays with HDMI input.   but your battery life will suffer greatly

Different.  and again..  I would lay out a custom board to fit all the accessory stuff you see hot-glued around the place.  you could consolidate a-lot of things that way

Nice job, it looks like the color LCD was meant to be there in the first place.

thanks Dan.  "meant to"  is probably a bit of wishful thinking it took a fair bit of hackery to squeeze the lcd and adapter pcb into into the existing screen case in a "tidy" manner.

Looks really good! I'd love to see some of the insides of it, I can't image how you fit both the Pi and the Teensy in there. I assume there isn't enough room for a battery, is there?

to call it a squeeze is probably mild. haha. as you hinted. I was working with some serious volumetric constraints,  started by fitting Pi by the IR port, keyboard membrane location determined the adapter board and Teensy location..   then USB hub, serial converter, Ethernet adapter.. various supporting circuitry for battery management and lcd back-light. and the full sized connectors all around fill the voids.  the Ethernet connector had to come from an old Xircom PCMCIA card to fit the depth constraints..  all while still leaving enough volume for the large lipo cell commonly found in large 3000mah 11.1 volt drone type battery packs. roughly  (35 x 120mm) (anything less and battery-life would make it pointless)     all in all it tight.. 

Edit:  i cracked it open and took a couple of pictures