How to write Good IDE?

[unDEFER via Digitalmars-d]

Hello!
So my unDE 0.2.0 is released 
(http://forum.dlang.org/thread/yzfthfipouzhejfskxxp@forum.dlang.org), and this means that the time to write unDE 0.3.0 - text editor and IDE.

And I grab my head when thinking how much I want to implement.

1) It must shows unused modules
2) It must shows parts of modules which used by module
3) It must shows not caught exceptions
4) It must autocomplete always even "string".to

I have seen pretty tool from Hackerpilot (DCD, dfmt, Dscanner), 
but it doesn't cover this list.

And I think how easier may be implement such IDE? From zero, or 
maybe possible to use parts of dmd/gdc?
And what important for you for Good IDE?