Notes and Exchange are very different products for different purposes. Microsoft can then stand back and watch all the developers flock to the new product. Microsoft could then blow Notes out of the water. Lotus Notes was, I believe, developed for end users. Programmers coming to Notes from other platforms cannot believe the development practices used in Notes.
Some events can be programmed, others are unavailable.
Programmers would choose this new product over Notes and users would have to follow. The one chink in the armor is that Notes has been around for a while and upgrades must be able to handle the millions of existing Notes databases currently in use. A new product, starting from a clean slate, could possibly overtake Notes.