I would understand your fears if Vue was going to switch to the new syntax completely. But with keeping the current syntax as a default option I think Vue won't become any harder to learn. In fact, right now the framework has plenty of advanced options like functional or renderless components or using JSX + render functions. Yes, they are niche and fully optional; so the function-based API will be.
I hope this help to resolve your concerns about Vue 3 learning curve ;)
Thing is, you dont know for how long is it going to be around, and not considered legacy.
I was about to teach vue to a junior coworker, will I be teaching him a way to code in vue that is doomed to be conidered legacy in a year?
It's already promised that object syntax will be around for the whole 3.x lifecycle (which is not less than a couple of years) and there is no clear promise to deprecate it in 4.x (which is not even planned so far). I think in a modern frontend development world where everything changes very fast, this can be considered as 'stable'.
In my honest opinion this scares me even more. Now I feel like when a newcomer is beginning to learn Vue they HAVE to know that Vue actually has two different syntax's. This is going to make it incredibly hard to get help. Just because both API's are supported doesn't mean they will be supported fairly. You have to be honest, resources aren't unlimited. At some point more resources will be spread to making the documentation better or the examples better for one of the API's. Chances are examples and code snippets being shown and kept up to date using both API's are rare in my mind. Every framework or language says they will. Guess what? every framework or language lies. They realize the resources aren't there.
I love Vue, but I'm just being honest: I do not think both API's would be treated the same. At some point it will cause a big separation in the community because some people are going to argue that the old syntax is better, while some people are going to argue that the new syntax is better.
I honestly think if you make a change like this, then you have to do it a certain way and saying you'll support both just isn't the way to do it in my mind.
To my opinion on the new syntax though: I can see where it can help and be easier to see what you actually have and where things are. But I can take the example from the original post (or even any example I've seem from the new syntax) and easily make it very hard to read and follow. I feel like they are acting like this just automatically makes components easier to read. They don't. It's 100% up to the person coding it to code them that way. You can write good code or bad code in ANY framework.
You have said it all
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