Came close to this OTL if you count Sicily itself.
The tricky thing is what to do about the Byzantines? They held a good chunk of the south for quite a while.
IMHO this implies a much weaker ERE, and also a Papacy that somehow hasn't developed a Holy War ideology early to deal with the raiders/heathens just across the border. If the Muslims are in a position to hold this much of Italy then you'd likely see a reaction from one of a number of different Italian kings to the north, many of whom claimed nominal overlordship of the southern Lombard duchies.