spoiler and thoughts time [+]

So. Bismuth. More column B than A, but this episode is a big one, and gives us a lot to think about when the rebellion and the war are in mind.
Homeworld is your standard empire, but a little more fictitious. They colonize planets, use them for what they're good for, and when they're done, they leave whatever might be left. Rinse, repeat.
It's funny they mention Ziggurat specifically. It feeds into the "pyramids were built by aliens" theory/joke, while also changing it up. It's not the egyptians who were helped by aliens (at least not as far as we know), but Sumerians, Babylonians and Assyrians of ancient Mesopotamia.
Rose lies. She lied to the gems and had hidden information from them on multiple accounts. Bismuth, Lion, her secret armory.
Taken at face value, this pretty much dashes away the Rose Diamond theories. Bismuth stated that she was just another quartz soldier who dared to be different. However, like I stated above, she has lied before, and it's still possible (though now highly unlikely) that she was, at one point, Rose Diamond. Steven telling the gems the truth about Bismuth and Rose's actions "made him better than her". While she was friendly, it's possible that Rose kept everything strictly on a Need to Know Basis.
Bismuth went MIA before the Gem Bomb. During what I believe was the last battle on earth, Bismuth took Rose to The Forge to present her final, gamebreaking weapon. She wanted Rose to use it to continue pushing against Homeworld until they arrived back on, well, Homeworld. Rose was against it, and fought Bismuth over it. Rose simply ended it there, most likely using her sword against Bismuth. Bismuth wanted to win, even if it meant that she'd be killing other gems in the process.
Gems have no idea how Steven is, or exactly why. Bismuth, though somewhat understanding of Steven's situation, was able to lead herself to the conclusion that Steven was simply Rose Hiding and lying again, much like what Japser thinks.