I listened to an interesting conversation with one of the Microsoft team responsible for the Spartan project: http://5by5.tv/webahead/94
Two things in particular were pleasing to me:
- The new browser (whatever it gets called) will be “evergreen” (meaning that it will update incrementally in the background like Chrome)
- IE11 on Windows 10 will include two rendering engines—the old one and the new one found in the new browser. So there’s some chance IE11 won’t become the IE6/8 of the future.