Having just presented a case for the possible rationality of the irrational decision of creating an Emacs-like IDE in Haskell, I wonder if we should not be even more irrational and contemplate the possibility of using Haskell to create a radically different kind of IDE.. New technologies are often used to imitate and reimplement the artefacts of previous technologies.
don't underestimate those "previous" technologies, though. given your outline, you're almost certain to find this interesting: Croquet is a powerful open source software development environment for the creation and large-scale distributed deployment of multi-user virtual 3D applications and metaverses that are (1) persistent (2) deeply collaborative, (3) interconnected and (4) interoperable. The Croquet architecture supports synchronous communication, collaboration, resource sharing and computation among large numbers of users on multiple platforms and multiple devices. http://croquetconsortium.org the screenshots can be misleading in their simplicity, so be sure to browse some of the papers referenced on the 'about' page in the technology section http://croquetconsortium.org/index.php/About_the_Technology
Up to you now, what is your dream?
if you look closely, you'll see that croquet is implemented in squeak, which in turn is a re-implementation of one of the ancient smalltalks. squeak is by no means the ideal implementation language for this kind of project, nor am i completely convinced by the synchronous approach used for croquet. but while implementation of croquet in squeak is obviously doable, i see various difficulties for doing the same in haskell. where squeak is too dynamic/imperative/flexible, haskell is too static/unreflective/limited (ever tried to pass functions through haskell's i/o interface? type Dynamic and dynamic loading are still outside the language definition [hs-plugins], as are distribution [gdh], persistence [many starts, no finish, but see Clean's first class i/o], reflection/meta-programming [Data/Typeable, template haskell..; meta ml?]). one dream would be successors to haskell and croquet so that croquet' could be implemented in haskell''. claus