Sincerely, I'm not so keen on the compared might of the Italian + AustroHungarian fleets vs. Mediterranean Anglo-French fleets to tell whether the Sardinia landing was feasible, I highly doubt about the Sicilia one, the Messina strait is too narrow, the CP fleets would have little trouble keeping it open, and if they can't siaolate Siciliy, a Birtish landing will end in a blood shed like Gallipoli.
Sincerely, I doubt the streategic value of occupying either Sardinia or Corsica, little manpower or resources of value, What are UK/FRance to gain from an occupied Sardinia, and for Italy it looks like Corsica is better claimed at the peace table, it would be a purely symbolic occupation, and unlikely unless UK and France suffer some catastrophic naval defeat in the North Sea and are forced to withdraw the Navies from the Mediterranean.
Strategically, Italy has much more to gain frocusing its efforts on pounding France on the Alps, possibly timing its offensives with German ones, so that France is obliged to exaust its reserves.
If anything, if the CPs want to do something really nasty, they could violate Switzerland's neutrality. Rich areas, ethnic claims for both Germany and Italy, it would force France to stretch the border to defend much further, French-Swiss border is not easy to defend, the CPs can attack it from three sides, making it undefensible. Belgium mk. II.