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).
The primary change seems to just be merging most of the keys/options (data, computed, watchers, etc) of the module into various functions within setup() which itself may require from coding best-practice guidelines since setup() is going to get pretty big.
I’d love to see a largish component converted to be able to compare the two instead of the small examples with one or two functions within it.
This will require one hell of a migration path to support and I imagine lots of people will be on that "Compatibility Build" for a long time. I'm very, very curious whether folks who have large-scale Vue apps have had a look at this proposal, and if they've had any input on it.