Interestingly, this news was leaked by blogger Zippo back in July, who accurately predicted the remaster. Of course, Ultimax was noticeably absent from modern platforms, not even being backwards compatible on the Xbox One as its predecessor was, so it could be considered an obvious prediction. Regardless, he predicted that only Ultimax would be coming, rather than both Arena titles, and the release would be next year.
On the night of The Game Awards, Zippo posted again, first gloating about his proven prediction, then casually mentioning "Oh, and Persona 3 Portable is getting a remaster. Multiplatform."
This release would be significant as fans have been clamoring for a Persona 3 Portable release for years, and Atlus has hardly acknowledged the game since its release in 2009. Despite missing the visual flair and explorable 3D environments outside of dungeons of the console release, Portable is often considered the best way to play Persona 3 due to the ability to control each party member, plus the addition of an alternate protagonist who alters much of the game's dialogue and story events, something no other Persona game has featured.