so, what IDE are you thinking about?

Eclipse => huge
Netbeans => idem
No java please it's not beginner friendly to have to install a huge framework. Maybe the KDE libs are better than having Eclipse, the java runtime, and all the mess to write a plugin, 68k asm support, etc.
Ant => maven => rather complicated. And we can generate build.xml or other things using a simpler 'master' project file.

Code Blocks? We have to write 68k assembly support, syntax highlighting. Using external makefiles is not an option. And this ide is made to be generic, it's not specific to gcc4ti and all his options, etc.

Others I don't know?

I'm starting to write some bits using Qt. Qt already has xml support, is not so big and is cross platform. This way, we can have all the features we need without dragging a huge "usine à gaz".
About the XML format, I want to make it simple, ie writable by hand. I DONT want machine readable XML that no one can understand by looking at it. It's a design decision. Do we really need an xml schema or anything like that? Even a DTD is sugar. The IDE can simply fail when it does not find the required xml elements.

Lionel Debroux (./6) :
(multiple targets, project groups, project dependencies, etc.)'

All these features are rather simple wheels if designed properly. I'm not fond of taking a lot of time to dive into an unknown code, we'll never find it 100% suited for our needs, and all the required fixings will be hacks, patches, and problems with upline synchronizations and etc, which will make unmaintainable code.

so let's agree on required features for the project format:
-human readable
-multiple projects runnable with a single command -> project groups
-relative filename support
-multiple targets with different file sets and options
-build has to be done on real FS paths even if files are displayed in virtual directories.