Since the topic of future Jouto is pretty interesting: I don't disagree at all with your wish to see Jouto itself expanded--I've wanted that for years, before and after HGSS. I got my wish for a full-sized Shirogane Mountain and can't tell you how ecstatic I was, but I still would like to see far, far more. In fact in GS Kanto did undoubtedly butcher Jouto--the evidence is apparent everywhere, with the real-world Chubu region being reduced to the area from Mt Shirogane to Route 31 or so, and the most massive part of Kansai being reduced to Route 32/33, a small town, and a forest. Even though HGSS Jouto was significantly enlarged from its original size in GSC in terms of tiles, and yet it was still tiny. So you're preaching to the choir here when you say we need a bigger Jouto--I mean, even simple things like a sea Route connecting Route 31 to Route 32, or another sea route connecting Route 34 and Route 41? Even the simple things would help.
On the topic of sequels, in fact aside from the reasons I mentioned, the other big reasons I don't see them returning to Jouto without including the region next door is that of Route 47 and 48. This is because that entire area is actually a premature extension into that very region; this is why Groudon and Kyogre are obtainable there with their backstory. Route 47 and 48 are the only area in the game where the Houen fossils are obtainable; likewise, Route 25--the northernmost route in the game--is the only place with the Shin'ou fossils. The reason why I personally expect them to release the region in between Jouto and Houen is because Houen hasn't seen a release forever, but who knows? I have almost no doubt that one of these two regions will be released in the near future, but there is actually a third option which I forgot about which could even align with your desire--they could make an entire region out of the Chubu area--the vast barren area with the Pokemon League and Shirogane Mountain.