Did seriously consider switching from Arduino to ESP8266 with program space as no 1 reason. After thinking about it for a while I decided to stick with arduino despite the limit of 32k program space. Reasons are mostly the time it will take to do the redesign and if I start a redesign every time I find a new shiny thing it will never be finished.
The current version will be limited in some ways but I rather add a arduino mega than switch to esp since that redesign would be just a physically bigger board than the current nano plus a ton of more program space. Going with ESP8266 means redesign a lot more, things like need more io pins, 3.3v to 5v level shifter and software changes both to make it work and also to implement the stuff I then would have space for - that will all take a lot of time to do.
For V1.0 it will be basically what I already have, a mainboard based on arduino nano, a separate lamp and keyboard plus a plug board.
If it is interest for more I may make a v2 mainboard based on ESP8266 with way more simulators included, things like UKWD, UHR box, all enigma models, custom models and more.