My "laundry list" of things I'd like to see for FSXI
Aircraft selection that would be a cross between FS9 and FSX. Maybe a thumb for the type aircraft, click on that, and thumbs for any variations pop out.
SDK compatible with the current one, but for my benefit, it should be written as something like SDK for Idiots, Dummies, and the Intellectually Challenged.

"Aircraft Adapter Tool" for importing and automatically upgrading or otherwise adapt an imported model from all the earlier versions of MS FS/CFS, and possibly form other sources and games.
I would like Photo-real terrain, but we have something like that on the actual B-52 simulator, but I don't happen to have a one terra-byte hard drive hooked up to my computer at this time.
Add-on Installer from the user interface, instead of having to fotch around with Windows Explorer. Installer could also handle tweaking .cfg's.
"Tweak-on-the-fly" for development. (For all I know, developers already have that capability.)
Terrain elevation scaler, so you can change the terrain relief, if you wanted.
Some sort of dynamic fractal generated cloud formation with real time development of clouds.
Really Nasty Weather. Like a hurricane, with actual hurricane structure, conditions and effects.
Little Details, like bug splats. Everything from little gnat splats to humungous, juicy beetles that make you want to declare an in-flight emergency 'cause you can't see out the wind screen.
More relistic terrain. Period! It's a sure bet the FSXI will be geared to what is now considered "high end" PC's, so they can afford to render more realistic terrain. For example, in Shreveport, the banks of the Red River does not smoothly transition from river to land. There's about a twenty foot embankment.
Or, at the very least, on that same note, "local customizing" of terrain through the user interface.
I'm sure there's more. :D