I liked the Sevii Islands, but they were essentially included in FRLG as a way to let the players know, "Yes, we know Johto exists right next door, but for reasons we cannot let you visit. But have this mini-region instead, complete with its own mini Johto soundtrack!" Since Hoenn does not have any neighboring regions, it's not like we can really expect something new to be made to make up for a lack of something else.
But at the same time, there is just so little information on these games that anything is possible. Depending on how much data space Hoenn takes up, there could potentially be a new mini-region (or even a full-blown region, but that's a stretch) in these games. I would only want it to be new and not the Sevii Islands simply because I want something to be unique to these games (Sevii Islands being unique to FRLG, and the Pokéathlon being unique to HGSS, for example).