While single roots per component etc are nice historical artefacts to leave behind, the composition API [1] is by and far the biggest change, and most impactful change planned for v3. Sadly the article only lightly touches on it in its last section. If you're either working with Vue, or interested in doing so, reading through the composition API RFC [1] is a good recommendation. It covers the why the what and the how, is easy to follow, and is well structured. If you're coming from a React background, this is akin to what React does with hooks, albeit the approaches are different in nuance.
[1] https://vue-composition-api-rfc.netlify.com/