Here’s the very original pitch doc for my first swing at XCOM, likely 2005 or so. Found it cleaning out old work junk. I use the phrase “Esprit de corps” in the doc so no wonder this version got canned. pic.twitter.com/dCIIDkw5DDFebruary 6, 2021
The fantastic XCOM: Enemy Unknown upended the strategy space when it came out in 2012, taking the well-worn turn based tactics genre and adding more stringent rules and less simulation in favor of a dynamic, manipulatable battlefield and soldiers with special roles and powers, rather than just equipment and numbers. Designer Jake Solomon has tweeted a picture of his very first pitch document for the reboot of the tactics series, from 2005, and it's very different from what was eventually released.
The pitch calls for a game in the legacy of the original X-Com, but with "action and role-playing elements" that aren't really present in the game as-released. The pitch specifically says that the reboot would have "suspenseful, squad-based, tactical combat" in "real time 3-D battlefields." That's something it absolutely didn't have on release—or ever. There are shades here of some kind of RTS, all the way up to the addition of vehicles to the battlefield.
The plot presented does have shades of ideas that would come to later XCOM games, however. The XCOM: Enemy Within expansion features an insidious human faction called EXALT, and the pitch does include an emphasis on fighting other humans who are "secretly aiding the aliens." Other key concepts, like randomly generated missions with destructible terrain, were present in the final design of XCOM: Enemy Unknown. For reference, this document was pitched in 2005, but an accepted pitch and development on XCOM: Enemy Unknown didn't start until 2008.
Speaking of XCOM, if you've never played it then XCOM 2 is on sale for less than $5 until February 18th, 2021.