Yeah, I would truly be surprised if IE was going to be killed off.

Here's my best guess. It's like Mozilla and Firefox. Firefox was originally a "streamlined, stripped down, super-fast" version of Mozilla. Spartan is much the same. They've stripped out all the legacy junk and it will be available as a standalone app for those that need no compatibility.

IE will still be provided for backwards compatibility, at least for a while... IE12 will likely have a compatible rendering engine with Spartan (although including legacy stuff which will make it heavier and slower). And use the IE Application frame.

Spartan will be the lean, mean, just the facts maam browser that has no legacy rendering support, and a simplistic application frame.

That's my best guess.