With Sevagoth having skipped Lavos for priming, I'm not sure, but the next slot (according to the apparently new MFMF etc. pattern) should be Lavos.
For context, we knew Xaku would be in an F prime slot, as they said that around their release. And prior to Sevagoth's prime breaking order AGAIN, primes were released in an MMFFMMFF pattern, very consistently, but then we had Protea following Gauss and Grendel, and then another male frame. So either there's no pattern anymore, or they've gone to an MFMF pattern.
