If you can only add ONE major update to Key Lime Pie, what would it be and why?

Though there's no rock solid information out yet, I think it's safe to assume that Android 5 will be released to the public in the coming months. In the foreground, there will probably be UI/UX changes while behind the scenes, there will be modifications to make the system run smoother and more efficiently.

If you had direct influence on the development team and can implement ONE major change/update, what would it be and why?

Me? Native support for proper backups. Android alone currently doesn't provide you with a decent backup. If my device were not rooted and I lost it or wiped for whatever reason, I'd be SOL. The two things I care about most will be irrecoverably gone; SMS/MMS and application data (such as game saves and app settings.) I think this is a major component missing that should have been available since version 1.x. Even 2.x. My first iPhone was the 4S and I absolutely loved the comforting fact that I could lose/wipe my phone yet have a useful, up-to-date backup to restore from. I know many OEM's provide their own backup solutions which are integrated with their devices and there are a few 3rd party solutions that require root to get the job done, but I'm referring to native support.