J-List and JAST USA boss Peter Payne has revealed that the translator working on the extra content from the PSP version is none other than himself.
(Also see my full review: [In-Depth Review] Seinarukana + Info Hub)
There will be no censorship of the [adult version of the] game whatsoever. And I'm happy to say the Steam version has extensive additional content, routes and scenarios and even some new characters. It's so extensive I've been staying at work til 1 am every night translating it.Source
Seinarukana's original content was translated by Aroduc of Seiha translations, who also worked on Littlewitch Romanesque as well as fan translation projects such as Kamidori Alchemy Meister. Aroduc declined to work on the extra content from the PSP version, further delaying a project that was announced back in 2011.
According to the JP Playstation store page, the PSP version of Seinarukana includes more than 35 additional CG, an expanded scenario, and additional voicework. Whether the adult version will include this extra content remains an open question. According to the Seinarukana Special Edition official JP website, the Special Edition includes both the H-scenes and the added content from the PSP version. That may or may not be the version JAST is working with.
Seinarukana's official site is up with a fairly nice trailer.