It would be a longer process, but I doubt Odo could muster the same amount of men as William IOTL to challenge a more unified England. IMHO it would be easier to conquer Ireland for him or a duke of Brittany than to conquer England. OTOH Ireland is rather decentralized, OTOH the most obvious alternative target, Scotland, is just too removed from Brittany.
Given all the restraints Ireland would have been the best option, though it could be a longer affair. maybe not the Norman conquest of Southern Italy and Sicily long, but with the lack of a real central monarchy it will be longer, yet IMHO it is a doable target. And a place, which unlike Brittany can make you an unquestioned king.