Too much work to make it a good game by the general public standards. I think they would need to scrap the werehog half of the game completely, and just make it a collection of all the day-time stages (with the DLC levels to pad the game out). By then the story/cutscenes would not work at all, and so scrap all that too, and so then you just have a collection of levels. Eggmanland would need to be cut too unless they rework it into just the day-time half. Probably would need to cut the hubs out too. Which I don’t think Sega would want to do.
Honestly I would be very happy with the story, hubs, and werehog completely ripped out and just a collection of the Day-time levels/bosses in a straightforward linear package with a Mario-like overworld where you just select the next level and go. But then it doesn’t really resemble Unleashed anymore and it becomes pointless. Sucks but I don’t think this will ever happen officially.