I really disliked the function API and felt the class API with decorators was much easier to read and work on.. I'm pretty sad they are doubling down on function API and, apparently, ditching the class API?
The class API will remain the current status of an add-on. The idea was that if we make the class API built in to the core, it will somehow be better than now and remove all the issues with it. More and more into the game it was turning out that's not that easy.
Even the decorator thing was problematic. Remember that the core Vue library is supposed to work both with and without build tools, but in case of TypeScript it's not possible. There is a decorator proposal for JavaScript but it works differently than the TypeScript one so there would be a clash.
In the meanwhile we found out a new solution that not only solves these but also some other problems (composability).
