The mangaka also tweet about it. This is the machine translation for her tweet.
"Sorry, it's not a typo that Seimei's fetish is a uniform! Originally, even in the manga, it was a very limited expression, so it was impossible to make it into the anime! However, the people involved in the anime have expressed Seimei's perverted nature and creepiness to the limit, so I'd be happy if you could enjoy it all over again!"
It's too creepy. A teacher who love girls sailor uniform. I never understand what considered as normal for Japanese standard. Tons of ridiculous ecchi anime with much more weird things happened exist.
I think that non manga reader won't able to grasp what Seimei fetish is. His fetish is not sexually and beyond that. It must be difficult for the team to use that troupe and convey what his fetish actually is with just few episodes without making Seimei look bad and ridiculous.
In the PV for the anime, they change the catalogue given by the principal to Seimei. From sailor uniform catalogue to uniforms catalogue. Apparently his fetish for sailor uniform is unacceptable and too much to be put in the anime
Wonder how they alter that aspect to make it works. I love that sailor uniform maniac