I'm sure your wife will love her new iPhone as much as you are going to love the DX coming off an Eris. The Eris has a more wide open bootloader, but it has other issues. I rooted a friend of mines Eris, and the lack of memory, coupled with the inability to move apps to the SD card almost drove me crazy!!!
Oh lordy will the DX ever spoil you with all that STORAGE! Click on the link in my sig and drool over all the apps I've downloaded. And I still have tons of room left. It's crazy man, crazy. I'm curious about one thing though... why on earth is your wife going to get the i4 when the i5 is SSSOOOO close? If I were wanting an iPhone I would have to hold off for that one.
Not that I'm trying to make you have to wait another 4 months to get your hands on your wifes X.
