Mithril uses Semantic Versioning (https://semver.org/) if I recall correctly. All the 2.0 signifies is that there are major breaking changes. If you're curious about those changes, take a look at the changelog: https://mithril.js.org/change-log.html#v200

Otherwise, the "big picture" hasn't changed since the v1 release. Mithril is a lightweight alternative to those frameworks that provides routing, auto-redraw, closure components, XHR utilities, reactive streams, and a testing framework out of the box. The v2 release has less to do with gaining market share or generating hype than it does refining an already great tool.