I think the sunroof is large enough for the Mo design, the only drawback seems to be woith the wind noise that you get at low speeds ( below 50Kph/30Mph) but a wind deflector will fix that issue. I don't know if they build a wind deflector for anything bigger in width.
I would also be interested on how a bigger sunroof would effect the Mo roof intergrity. Most factory sunroofs are designed that IF there is roll over that the roof will not collapse upon the passengers.