So, of the possible targets that have been named...
The Ninth is Aaroniero, the swiss-army-knife former Gillian. He eats other hollows for their powers, and has a giant, unpredictable array of abilities he can pull out to hose people.
The Eighth is Szayel, the mad scientist. He's constantly spying on everybody, and has all sorts of mad science nonsense he can pull out on short notice to hose people. Also, he's clearly integral to Aizen's plans, since he's been put in charge of the Six-Million Dollar Yammy project.
The Seventh is Zommari, who, frankly, has no obvious characterization whatsoever, but he's loyal to Aizen. From outside the quest, he's super-fast, and has beams to let him control objects, people, and parts of people.
All of those are terrible targets. First, because Cirucci is already getting the stink-eye for knocking off Yammy, one of Aizen's strategic weapons, and two of the potential targets are more of the strategic weapon crowd. Second, because all three have the potential to just no-sell fights on short notice, if they manage to pull out the right trump card, or if Zommari ASSUMES DIRECT CONTROL of something important. They're not opponents who you can count on beating just because you're a beatstick. Third, because Luppi is obviously a treacherous weasel, and we can't trust him, and have no reason to do him any favors.
And, frankly, if Luppi is as hungry as he's suggesting, Cirucci doesn't even need to act. She's protected from Luppi, for a while, so he'll have to go after a higher-ranked Espada on his own, and he can suffer the consequences himself. If he wins, fine. If he loses, it's a chance to learn something useful about the survivor if we decide to revisit this decision later.
And Cirucci has only been in the Espada again for one day. Time to sit back and enjoy the privileges of rank a little, lady. If you were going to bump off the Ninth anyhow, you should have gone for him initially, instead of wasting time on Yammy. You got the win. Don't throw the win away for dumb greed.
[X] You disagree.
I really don't see a whole lot of upside to further rank-climbing any time soon. It's just going to confirm everyone's worst suspicions about Cirucci, build animosity, and weaken Hueco Mundo's forces right before a war we've been told is incoming, and for not much gain. Who is waiting in the wings to challenge her right now? Not Luppi, he's on time-out. Not the other Privarons; they are outclassed, and know it. It'll take them a few months to train up enough to make a challenge, by which time the whole situation might be different.