The games won't just receive a glossy high-definition update.
According to what Square Enix producer Yoshinori Kitase told Siliconera , the upcoming Final Fantasy X/X-2 HD remasters will feature "the most complete version of FFX-2 ever released in the US."
This includes all the content from the PS2 re-release along with FFX-2 International + Last Mission. Plus, we can expect additional dresspheres and the Creature Creator will be featured as well. The latter is similar to the Paradigm Pack for Final Fantasy XIII-2 , in that it lets players capture monsters and use them in their party. So, you can use any monster you nabbed in place of Yuna, Rikku, or Paine. FFX characters should be available, too; Lulu and Kimahri could be options.
As for the new job-changing costumes, they could be the Psychic and Festival-Goer dresspheres, which were on display in this YouTube video:
Related Game(s): Final Fantasy X/X-2 HD