We will be making a public road map of things happening in Vue, to make it easier for you to keep track.
Vue 3 is going to have little API changes - the main difference is it will only target modern "evergreen" browsers (i.e. IE11 & below are out).
What are the benefits?
Reactivity system will use ES2015 Proxies. This will get rid of most if not all of the caveats in the current reactivity system, and should improve performance as well.
Internal code size reductions: there is lots of code dealing with compatibility. All if this logic can be dumped.
v2/v3 will be maintained in parallel with feature parity until the older browsers completely phase out.
It will mainly be a choice of what browsers you support.