I read on Italian press about new rules for luggage on Trenitalia high speed trains (Frecciarossa, Frecciargento, Frecciabianca).
From March 1st: no more than two pieces of luggage for each traveler.
For people traveling in second class (or Standard, or Premium), the sum of the three dimensions of each piace of luggage (height + lenght + depht) should be no more than 161 centimeters (no single dimension more than 80 cm)
For people traveling in first class (or Executive, or Business), the sum of the three dimensions of each piece should be no more than 183 centimeters (no single dimension more than 120 cm)
You can add a music instrument or a stroller or a wheelchair, as long as the sum of their dimensions is no more than 200 cm. Each piece of luggage should be labeled; no luggage in aisles or near doors.
Luggage not conforming to regulations will be fined (50 euros) and will have to be removed from the train at the first stop.
New rules (in Italian)
https://www.trenitalia.com/it/informazioni/la_guida_del_viaggiatore/la_sicurezza_deltuoviaggio.html