Titles are account-wide. Pets and mounts are account-wide. Toys and heirlooms are account-wide.
But you know what I REALLY want to be account-wide?
Because as is I have two characters with Tabard of the Argent Dawn but my current main doesn’t have it. Just my luck, right? But yeah, I would LOVE to be reunited with it. I’ve already been reunited with my Vampiric Batling and Spirit of Competition. Tabards next? Please Blizzard?