Flashbacks are great: they’re typically very pertinent to our interests, being about stuff we’ve wanted to know about for a while. We can also hope they might foreshadow the arrival of new characters.
Was that Bismuth?
The question everyone is asking: was the Gem that poofed Lapis in her flashback the same Gem that we see bubbled in Lion’s mane? It’s definitely possible: the multicolored hair would go well with real-world bismuth, which the bubbled gem looks like, and the L shape that sticks out could possibly fit with what we’ve seen (though the angle we’ve seen it at isn’t ideal). Also, the Gem shown was quite muscular, so if anyone has room for such an enormous gem stuck inside her, she could.
Approaching the flashback as part of a cartoon (rather than treating everything as “real” like we prefer to), it would definitely make sense if the writers wanted to foreshadow a character we’ll meet later. If it’s a bubbled gem, then whoever is in that bubble in Lion’s mane was obviously important to Rose, and is meant for Steven to deal with at some point, and an early look at her would be a fun little easter egg for them to hide (especially if she’s corrupted, so we won’t see her regular form at first).
However, there’s just no way to be sure. For all we know that might not actually be a Gem in Lion’s mane. Until we get an answer though, you have our permission to wonder away.
After Reformed people noted how much faster Amethyst was able to reform than Pearl (getting close to a hundred times as quickly, though both Gems’ times were for long reformations), and it was pointed out that Amethyst is meant to be a soldier (while we now know that Pearl is meant to be a servant). Considering how quickly Amethyst is capable of rushing her reformation and still being in fighting form, it would be a very useful ability for a soldier on the battlefield.
When Lapis released her physical form after being struck, in a battle that the homeworld Gems appeared to be losing, she still had not reformed by the time a soldier loyal to the homeworld showed up to police the battlefield. This points to a long regeneration time (though it’s always possible that the homeworld forces later rallied and kept the field).
Who are the Crystal Gems?
The very fact that the homeworld simply assumed Lapis was a rebel is also interesting. Sure, it’s entirely possible that they simply saw a Gem they didn’t recognize and assumed her to be an enemy (as the Crystal Gems apparently did as well). Moving on to more fun speculation though, we saw that the homeworld Gems in her flashback were quartzes, created to be powerful soldiers. We don’t know much about the Crystal Gem armies, and the very few members we do know of are not created to be soldiers at all.
It would be very interesting if the reason Lapis was assumed to be a Crystal Gem was the fact that she had not yet reformed: the homeworld is only fielding soldiers who will be back on their feet in a matter of hours (if not minutes), and if their enemies are primarily not soldiers and if non-soldier Gems take far longer to reform, then an undamaged gem not yet projecting a physical form would probably be assumed to be an enemy combatant who had been hurt in battle.
If they had lost the battle, and were only back on the battlefield days later, they might have considered themselves lucky to find a gem that the rebels had “missed” (for retrieving the gems of your fallen comrades would certainly be a normal thing to do if able). They probably didn’t have any other prisoners from the battle, as Lapis indicated that they interrogated her for a long time; remember, the magic of the mirror she had been placed in compelled her to answer, so any Crystal Gem given the same treatment would have told them what they wanted to know and they would have stopped asking Lapis the same questions.
The galaxy warp
Even when we’re getting to things we’re wondering, we’re still surprised by things about the galaxy warp. Not only was it active during the entire war, but it apparently took a while before what was left of the Crystal Gems made their way to the galaxy warp (Lapis said it was “ages” before they took her).
It does make sense though: the shock of the homeworld’s bombardment of the planet, and likely a lot of monsters to deal with and not very many Gems to do the dealing, would make checking out the galaxy warp a rather low priority. After all, the homeworld thought they had won, and as we saw taking out the galaxy warp only makes coming to Earth inconvenient, not impossible. Still, given how important the Crystal Gems considered making sure the galaxy warp was still offline to be after Lapis escaped the planet in Ocean Gem, we would have expected a bit more hustle than what it seems like we got.
We don’t know how long “ages” is, but Pearl had apparently changed to her “young Gems” outfit that she was still wearing when Rose first met Greg. That apparently narrows it down to no earlier than 500 years after the end of the rebellion, since Amethyst spoke as though she had seen Pearl regenerate at least once – if not multiple times – but Lapis was probably there for thousands of years before the Crystal Gems finally made it to the galaxy warp to disable it. Yikes.