I've been playing the pre-release builds a bit and one of the main things I noticed is the motion tracker.
11 February 2011 - The motion tracker was always on your screen, unprompted. Shooting would make it disappear until you stop shooting for a few seconds. No motion tracker if you held a pistol or grenade/acid spray. There was no toggle to turn on the motion tracker either.
No HUD if it's stowed, detecting aliens.
This motion tracker POV can be seen in... 2008 magazines? Or 2009, around that.
10 March 2011 - The motion tracker adopted a more final look POV. Except marines were marked in green, enemies in red and ammo caches in yellow. No objective direction.
You had a HUD that would state the exact number of enemies detected by the motion tracker if it's stowed. It seems like they had decided to provide such HUD very early.
July - November 2011 - Ditto

About
a year before release, the motion tracker mostly adopted how it'd look in the final release as we know. All targets were in white dot.

Thanks for checking out the thread!