It wasn't abandoned with the 355. The 5 in the end is referring to the quintuple valve system that were the highlights of the car at the time. I concur, 360 and 430 didn't follow the nomenclature strictly, but at least you still know what size engines they carry (and obviously it will be a V8). Traditional or not, it has been used in 50+ years of the company history with only a few small deviations here and there, and it's a nomenclature that makes most sense and objective (compared to the alphanumeric soup used by Merc/BMW/Audi that keeps changing and oh look Cadillac has just changed its nomenclature again, thanks GTP News for telling me).
Anyway, since neither you or I are in charge of naming cars at Ferrari, F8 Tributo it shall remains.