Designing a better UI framework with MVVM

Talking about common problems with game UI and developing UI framework (the layer between UI and Gameplay systems). Describing and understanding MVVM pattern and which UI systems for game engines support it. Introduction and first steps into designing UI framework, areas on which to focus first, and how to separate certain logic into more comprehensive subsystems and type of abstraction that you'd like to introduce. Do's and don'ts of designing a UI framework, and a common description of an event-based design, with possible dive into a data-driven implementation on supported UI systems.