we've had this kind of discussion over at vdip too, about stagnation, shrinking and how to recruit and hold(!) new players.
there were many things said that were absolutely true and desireable, and i pointed there on an aspect where my profession lies and i may be able to actively help:
from my experience, when recruiting people i know they love strategy board games and they are being defacto "always on" and therefor are spot on target group for diplomacy, one major feedback was about the interface.
a) it was said this is feeling, looking and (by far most important) playing like browsergames from 1999 (we've played that a lot and liked them back then). for me as a long term user, the interface does not hinder me at all to play diplomacy here or on vdip (well, i have made my interface adjustments to see more same time than the standard layout provides), but it's obviously giving a bad first impression to those who may be interested but not familiar yet. some were scared away fast, others stayed, accepting the current state and seing it's somewhat okay once dived into it.
This is not at all about looks, but about streamlining all things that are regularly done in this game – collecting information about the state of a game, communication, setting orders, viewing the map, which all has a lot of potential to improve with the knowledge of user experience and interface design from the last decade ...
b) after NMRs of new players i recruited, the reason given was very often: "i was online on my mobile only and would have wanted to set orders, but setting up was so tedious there i just gave up, sorry".
Now i know if someone says "mobile" and "app" many alarm bells ring, as diplomacy is far from being a casual game app by it's design. anyway, while improving a), a lot could be done to make b) less of a hurdle. No need for "apps" and fancy stuff giving a wrong impression about this game, but making the interface better on desktop screens will help making it better on mobiles too.
i'd be willing to actively help with interface design and implementation (it's what i earn my money with) if there is interest and coordination present. two and a half years ago i posted this on the webdiplomacy.net developers forums, but this never got traction ... http://forum.webdiplomacy.net/viewtopic.php?f=12&t=1696&sid=a355bd3c989ed2b69cf44d61d33843d3
As this is still lying around as a potential starting point (no final result!) i thought i'd give it another try when reading this topic here.