Rice is a great pairing, I was served a dinner of roast lamb and rice 4 ways recently. Each rice added it's own unique taste profile but still let the roast be the star.
As mentioned Garlic mash/smashed potatoes are an option but remember the braised shank will be unctuous when you are deciding how much creamcheese/dairy to add. Polenta is always a good choice for a crowd as are pan roasted rosemary/herbed potatoes. Oven space management is at a premium so you might think of looking to par-cooking some sides that could be reheated quickly perhaps under a broiler like asparagus and mushrooms. Ideas for cooking for a crowd is dictated by kitchen logistics more than by imagination.
|running is better|
i actually meant to say sour cream and not cream cheese.