The art for the teachers, mia and many other characters isn't completely redone. The bottleneck is definitely the art. A new coder won't do much.
The coding is the bottleneck. The remade art was never meant for the tech update. It was for after the tech update when each character would get their route and art touched up. The tech update was for making the game wide screen and fixing the spaghetti code so that future updates could come out faster. But with how long it’s taking to do that they’re remaking art and rewriting stories in the mean time since DC (artist) and Sploosh (writer) have nothing else to do.
For the tech update they have to rewire all the routes, repose every scene, and redraw all the same art since they were static images without layers before which meant every scene variable required a whole new image to be created. They’re now turning each art asset into layers to make modified backgrounds and poses easier in the future. Most of that is already done though. For coding however, since every route can be done in between every other route, they have to code for every possibility in order to prevent route collision issues which is why the rewiring is taking so long.
DC has already completed a crap ton of art for future content while waiting for coding to be finished. He’s done art for Judith and her mom, Annie and her mom, Ronda and her mom, Coach Brigitte, Cassie (renamed Zoey), Missy and more. They said they wanted to remake many of the oldest routes like Jenny, the teachers, Debbie, Tammy, and Mia which is what they’re currently doing.
The reason the tech update isn’t done yet is because Stray hasn’t finished rewiring all the routes for the already completed content in the new engine. Once that’s done, we’ll able to play the old content in the new engine.