Unmarked spoilers! Beware.
[[WMG: Unohana is the possible Vasto Lorde Ulquiorra mentioned in Chapter 7.]]
We know from Grimmjow that she was experimented on- presumably, Hollowfication- and then escaped. She's one of the strongest Captains, so Ulquiorra could easily evaluate her as possibly a Vasto Lorde. Since she escaped, she may not be as far gone as the Hollowfied shinigami seen so far... but we don't know what state she's in, either physically or mentally.
[[WMG: Suzumushi will reappear. It will be a major OhCrap moment.]]
So far Suzumushi has been mentioned twice. In Chapter 5, during his conversation with Sasakibe and Nanao, Ukitake mentions that Tousen's zanpakutou originally belonged to his friend, and that he was allowed to wield it despite the usual rule that zanpakutou must be buried with their owners. In another chapter it's mentioned that Aizen had Suzumushi, but not Tousen's body, returned to Hueco Mundo- meaning that he presumably had something planned...
* Well, Suzumushi did show up, and is linked to Aizen's Hollowfication experiments... but Suzumushi itself doesn't seem to be an actual threat, and most of the "OhCrap" came significantly before. Although Suzumushi is actually trying to mess with Nanao's head and maybe use her to take 'vengeance'. Only time will tell what she's up to.
** If her reactions to her in Chapter 43 are anything to go by, Nanao doesn't seem to have as much control over Suzumushi's influence as she seems to think. She tells herself she's ignoring the Cricket when [[spoiler: they find Kyoraku's cell but once freed he immediately notes that Nanao is 'fondling' Suzumushi's hilt without even realising it.]] While Nanao claims and is probably right to think that Suzumushi could be of use, the spirit could also be a threat to Nanao.
[[WMG: Tatsuki will become a shinigami.]]
Provided that the Gotei 13 survives in any way at the end of the fic- and that the world does not end- they will need new recruits. Tatsuki had some ability to sense and manipulate reiatsu even as a living human. She was killed by a clone!Nemu, and her spirit did not remain in the vicinity, or Yoruichi would've noticed. Since Tatsuki did not die immediately, the Nemu seem not to have the power to destroy souls- so odds are she made it to Rukongai. Which is a nasty place right now, but she's got a chance.
** Her spirit did stick around long enough for Isshin to perform konsou, so she's now in Rukongai.
[[WMG: Suzumushi is a threat to Nanao]]
Nanao is being influenced by Suzumushi more than she is willing to admit. It's her refusal to accept the thoughts of vengeance that means that the Cricket's affect on her hasn't gotten past Nanao absent-mindedly touching the zanpakuto's hilt. It may not stay that way. Because Nanao's own zanpakuto is apparently unwilling or unable to respond to this sort-of Demonic Possession, Nanao will have to do it herself in an 'inner world' confrontation of sorts. Clearly we're not done exploring the nature of zanpakuto-shinigami relations, and this would be an interesting way of looking at it.