Ignoring graphics cause that's due to limitations, I'd say Sinnoh is the region that needs a remake the most. The region needs an overhaul so it can, ya know, actually stand out. It's so BLAND. And Diamond and Pearl specifically are so slow. I want to see the Distortion World, and a lot of other stuff, so I think I'd rather it just be Platinum remade.
I honestly wouldn't mind one. I enjoyed Gen 4, despite it not being particularly standout. Perhaps with a remake, we might be able to find something to give it a bit more oomph. And i'm not going to lie; the idea of using the underground as our "festival plaza" if you will is a strangely curious one that I kinda really want to see.
Oh gosh I'd love a remake, especially with the udated 3D graphics. It would be so cool to see such a big game redone that way. As most everyone in this forum, it was my first main series game as well and I'd very much adore a remake. As for me personally I had Diamond and Platinum. I don't think they would remake Platinum seeing as for ORAS they didn't remake Emerald, though who knows.