First, somehow Tamaki forgets about Shiraishi's identity. As he's no longer a Witch Killer, any form of Memory Wiping is now possible on him. In addition, we can now confirm the theory that each Witch Killers were assigned along with each groups of witches, and lost his power when the group lost their.

• Yamada -> Nancy's group
  
• Tamaki -> Shiraishi's group (all lost their power)
• Ushio -> Takuma's group
  

Second, the chapter 233 confirmed another theory that Odagiri got her charm power because she wanted to be love and respected which is very similar to Hikaru's.

Third, Takuma's double powers. It's both unique and unusual so far for a person to hold multiple powers at the same time (albeit with two personalities). It's currently unclear if the "real" Takuma can use Amnesia Power or not, but the Personality Swaping was likely placed on him to prevent him from initiating the ceremony under normal mean since his ambition is evil (you can't hold ceremony with only six witches). As he's considered evil, he probably doesn't need to kiss to use his power either.

Finally, chapter 235 basically screams "we're at the start of a possibly long final arc". Yoshikawa had given us most of the answers from the first and the second arc. However, few keys and several from third arc aren't given yet.

• The reason why Yamada, Tamaki, and Ushio became Witch Killer in the first place. Also, what's Witch Killer?

• Are there still any hidden/removed/destroyed memories from the first year?

• More focus on several characters (read:Ichijo, Hino, Akane), please Yoshikawa..

• Ultimate explanation for the background of the Witch Power

• Why Suzaku is ruled by the Student Council, and no Pricipal or alike in sight (so far)?

Last, some of my own speculations of what's going to happen.

• Shiraishi disappears somehow.(likely) Most likely, all except for few are able to remember her.

• The mastermind could be anyone who benefits from her disappearance but most likely, those who want to beat her in school grade(?) or those who had feeling for Yamada. Alternatively, "she" wants to disappear from Yamada's life due to an unknown guilt(she did try to take blame for the arson back in Maria Arc after all).

• However, the cases of erasing memories of a single person only occurred on Witch Killers, so this is extremely unusual. Yamada will probably consult with Rika and Nancy.

• Yamada's still likely to suspect Takuma. We'll probably get the rematch soon.

• This is Yamada's race against time before the graduation, as all the Witch Powers will relocate again after most graduated, and he'll definitely lost his Copy Power for real.