I doubt a bigger screen, it would be very hard on the battery. If it's true, I'm going to be extremely pissed off that Nintendo will do the same thing as they did with DSi and announce a clearly superior version extremely close to it's original launch. Why couldn't they offer this huge version when 3DS launched ?
DSi XL is more of a preference thing and not a clear upgrade. Some people like the larger screens and system. Others think it's too big, bulky, and the screens make the games look bad.
Personally I think the XL looks great but I never bothered to get one.