I have been spending some time taking a fork of a fork of the Arduino IDE (originally forked at 0023 and passed through being MPIDE since then) and done some big changes to it.
I have ripped out a huge amount of the internal code and completely re-written it.
It now supports multiple different board types (not just Arduno, but anything else you can think of too) through pluggable "cores". It has the Arduino 1.0.5 core in there at the moment as standard, and you can download cores for other board types too.
Boards are now completely self-contained folders, so creating and distributing your board settings is now a doddle.
There's even a powerful plugin system, so you can write plugins in Java for it to extend how it works - I've written some already.
Libraries, cores, boards, plugins, etc, can all be installed through the menus, so no messing with finding the right folder.
I have written a new serial terminal interface specially for this - it supports full ANSI colour and cursor controls, and sending of individual key-presses - just like a "proper" serial console.
I have also written a "graphing" plugin that allows you to draw pretty graphs using just a few simple serial commands.
Also, the system is completely rebrandable to suit your needs.
I've named it "UECIDE" - "Universal Embedded Computing IDE".
I've reached a point where I want people to start having a play and see what they think and tell me what's not working right.
Read more at http://uecide.org
Oh, and if you want to help out, why not fork the repo and have a play with the internals? https://github.com/majenkotech/UECIDE