In the alpha-stage, Generals was supposed to tie into the Tiberium universe. You can find many early Generals concepts with a lot of Nod units drawn on them. Most Chinese units at the time also bears the Nod insignia. There was some quite distrubing, but clearly Noddish unit design, too, nameably, Kane's head in a jar.
The original Generals planned to have players choose a specific general from their Command Center in-game before they could start base-building, this idea was scrapped due to time constriants. Zero Hour re-implemented the idea, but instead players choose in the pre-game menu instead of in-game.
In the beta stage, each side was able to "subdue" enemy infantry with a specific weapon: the US uses flashbangs, Chinese had stun bullets and the GLA employs tranquilizer darts. Subdued enemy units will fall under the captor's control, who can then load them onto POW trucks to send them back to POW camps, where the prisoners are used to "power-up" the player's special power, much like how Nod Chemical Missile logic worked in Tiberian Sun. The POW logic is broken and unusable in the final release, but assets for all the POW trucks and POW camps are still largely intact. Rangers still ended up getting the Flash-bang upgrade, but it now works purely as an anti-garrison/anti-infantry weapon, yet they kept the "Subdue" voice when using this attack. More on the POW logic: The original idea was for players to send the prisoners back to the POW camp to power-up a specific power, and also receives a small amount of cash. The more prisoner the player sends into the POW camp, the longer the duration of their special power will be.
The US could activate the CIA Intelligence power from the Detention Camp, which allows them to see what their enemy can see for a brief period of time. The Detention Camp is still buildable in the original Generals, but without the POW ability, and the CIA Intelligence power became a normal special power which requires cool-down. Zero Hour completely removed the Detention Camp and merged the special power into the Strategy Center.
China could activate the Defector power from their Propaganda Center, which can be used to convert enemy units to your side. The Defector logic still exists in the final game, but it changed to convert a random unit from the enmy, which causes huge balance issues, as a result very few mods would re-enable this function.
The GLA Prison could activate the Demoralize power that rapidly reduces affected unit's firing rate. The Demoralize logic is marked "Obsolete" in the final release, but is in fact still workable with a few tweaks, although it now affects your own units as well.
The Red Guard used to have a bayonet which it could use to stab enemies. The code and cameos are still there and can easily be re-enabled.
The Zero Hour expansion's General's challenge was originally planned to feature a "boss general" for each side, each would have the special units of their sides generals as well as what the vanilla version of the faction had. Two of them were scrapped, however, with only Leang making it into the game, even though quote for the other two were made and are in the game's the sound files.
The Superweapon General in Zero Hour originally got the ICBM and Tomahawk Storm in addition to the Particle Cannon. The code, cameos and models are all present, but partly broken.
In the planning stage of Zero Hour, Dr.Thrax (Toxin General) and Prince Kossad's (Stealth General) faction would very different from their skirmish selves. Thrax had a unique model and cameo for his RPG Troopers, and his infantry are immune to toxin and radiation, while Kossad had almost all of his units and structures stealthed off the bat, was able to build up to 5 Jarmen Kell hero units, and holds the unique "Quad Sniper" upgrade which allows his Quad Cannons to fire sniper shots, instantly annihilating enemy infantry squads. The player still encounters this version of them in the USA campaign and GLA campaign respectively, and much of these assets can still be placed on the custom maps using the World Builder, but are otherwisely inaccessable in Skirmish games.