Safari Extension or Safari App Extension?

A client of us needs an extension on Safari.

Now we see 2 methods to develop a Safari extension;

1. (Old) Safari extensions (written without XCode in Javascript, HTML and CSS)

2. (New) Safari App Extensions on an (Mac OSX) app (written with XCode in Swift, Javascript, HTML and CSS)

According to Apple's site "The future of extensions development takes place in Xcode"; so the second option seems to be the most future proof according to Apple?

However when I search for Safari App extension on the Mac OSX app store I only see a limited list of Safari App extensions. After trying a few free ones they also don't seem to work; after activating they don't seem to do anything.

Although when I search for option 1; (Old) Safari extensions, then I see lots of extensions that can be installed in Safari.

So it seems there isn't much interest from app developers to support this new Apple way of building Safari extensions in XCode, or is it too new?

Can anyone answer me these questions?

1. For what time span into the future will Apple still be supporting these Safari extensions without an app?

2. Should our client stick to old Safari extensions for the time being, or is it better to shift to the future XCode way?

Thanks alot.

Reinier