I have played a bit of online Dip in the past, mostly at Bounced, and have also played a few face-to-face games.
I've recently become interested in board game design and I have started designing a new board game that has many parallels with Diplomacy, including the core mechanic of simultaneous ordering. The game is set on a struggling planetary colony, where five factions are fighting to get control and save the planet from famine and from each other.
Differences to standard Dip:
You have to manage an economic engine, not just Supply Centres
You can trade resources
Different parts of the map have different values to different players, based on which resources they need
It is possible to win without concentrating on military conquest
Solos are not possible, by design - you need to share victory with one ally
There is a spherical map with no safe corners and everyone interacts with everyone else
Some fog-of-war with units on secret Location Cards instead of the map
Uses a worker-placement mechanic a bit like Puerto Rico
Designed for five players
Mess up the diplomacy and you are dead
Need to balance trust with skepticism
Simultaneous military orders
If anyone is interested, please contact me.