Hi, my idea/dream would be:
Split GUI strict from operative Gnutella code, highly object orientated.

That way it would be possible to have clients on multiple targets, e.g. have a KDE client (using KDevelop) for Linux and a MFC client (using MSVC) for Windows. Yes, I'm not a Java fan.
Also it would be possible to give a GUI for beginners (Xolox like) and a more nerd orientated GUI for those who need more control (maybe a console client, which you can control with shell scripts).

Hope it helps, Moak