If NISA can't do it, the best way to go about it is to make a fourm and support it on both the Official Sega and Miku Facebook pages.
The Miku one is here and is run by OFFICIAL Crypton staff (This is the page that inspired them to create an english voicebank): https://www.facebook.com/pages/Hatsune- ... 637?v=wall
If people show they really want it, Crypton will notice it. Crypton/Sega so far have been extremely kind to their English Vocaloid fanbase- going as far as to bring over live concerts and make an English Miku voicebank (Both being extremely pricy projects). The reason that they didn't release the other vocaloid diva games is because PSP isn't so popular here. 3DS does in fact have a chance, so push for it guys :>