Hi Ant,

Happy New Year and thank you for the question. The last two days I'm thinking about the same thing - about our products and UIkit v3

Now, I will explain everything in great details so we can forward other users to this discussion and have it as a reference.

The short answer - Yes, we will update the "UIkit for Gantry5" atom to UIkit v3 and we will update all our products to make them compatible with UIkit v3 but it will not happen before the summer.

The long answer - UIkit v3 is still in Beta. The components that we use the most in our products (Slideshow, Slider, Slideset, Parallax, Lightbox and Dynamic Grid) are still not available in UIkit v3. This is written in the official announcement of UIkit v3 as well. We cannot do anything before UIkit v3 is out of Beta and in my opinion it will be in Beta for at least 2 or 3 months more.

UIkit v3 is a complete re-write of the framework and it works in a completely different way compared to UIkit v2. Many class names have been changed and all data attributes have been renamed. The way you write the markup (in order to use the features/components) is completely different.
It means that we would need to re-write the whole markup of all our products in order to make them UIkit v3 compatible. And when I say "to re-write the whole markup" I literally mean that we'll need to re-write it all.
And that's not a problem - it is awfully a lot of work and it will take us quite some time to do it, but we are willing to do it and we will do it.

The real problem here is - the Backward Compatibility.

What we are planning to do is to re-write all our products (templates and particles) with the UIkit v3 markup and release a major new version of each product that will NOT be backward compatible with the previous version. For example, we will release v2.x of all our templates that will not be backward compatible with v1.x. And we need to do everything in a perfect sync, we need to release the new version of the "UIkit for Gantry5" atom, the new versions of all particles and the new versions of all templates at absolutely the same time so there are no customers that will download a particle written for UIkit v2 and try to use it with the "UIkit for Gantry5" atom which will load UIkit v3 and vice versa.
And here comes the tricky part - our templates and particles will be re-written and the "UIkit for Gantry5" atom will load UIkit v3. So far so good, our templates will work perfectly fine in a new installation. But what about the old users that will update their template from v1.x to v2.x? What if they have an override of some of the particle files in the custom folder? Then those particles will simply stop work and the only solution would be the user to re-create the overrides.
An even worse example - what will happen to the users who have used the UIkit v2 markup in their articles and Custom HTML modules? Everything will be broken and they will need to edit each and every article and change the markup on their own in order to fix their websites.

I'm writing all these things so you guys can see that it really isn't that simple. We do need to think about all scenarios and all possible side-effects of this change and come up with a solid and well thought action plan.

All that being said, let's have a look at what UIkit v3 actually offers. Well, there are almost no new features that you can use together with Gantry 5. The new features that UIkit v3 offers are supposed to be used when you build an entire HTML website from scratch. The new features are mostly related to the Offcanvas, to the Menu, to the HTML Editor and DatePicker... all those things come with Gantry 5 by default so you cannot really use the ones from UIkit, there's just no point.
What UIkit v3 is all about is that it is now even more modular and its code base is more future-proof. That's all. The features are pretty much the same as in UIkit v2.

You said that the UIkit documentation is now for UIkit v3. The documentation for UIkit v2 is also there and it will be there for at least two more years:

https://getuikit.com/v2/

Well, that's it for now. I hope that I answered your question