Long story short: there is no official way of getting truly custom watchfaces onto the Apple Watch
While we are still longing for an official way of creating our own proper watchfaces on the Apple Watch, it is still not possible at this moment in time.
Many developers have thought about how to still get their own watchfaces onto their Apple Watch but most approaches - while looking great - are simply not a good experience and very cumbersome to use. This comes down to the fact that every approach is basically just a workaround to somehow bypass Apple's strict rules and regulations.
Yes, there are watchfaces which are completely custom and fancy looking (as pictured on the image above) but they are not real watchfaces but only an app which needs to be manually launched on your watch, completely defying the purpose of a watchface. Whenever you get a notification, it closes the app (and therefore the watchface) and you have to manually reopen it. Same happens after a certain amount of time (because Apple ends the process) or when you press the crown.
This is much too cumbersome and not practical at all.
The approach we use does not have any of these problems and is even fully compatible with the Always-On display of the Series 5 and newer. It is an actual watchface and is always visible. It is not affected by the problems we mentioned beforehand. Our approach actually makes use of the complications on a watchface and what we are actually doing is just designing these complications in a fancy way.
Given that we are bound to Apple's watchface templates, there is only so much we can do. For example we can not reposition the time itself and only make use of the available, predefined slots for each compilation - outlined in dotted lines here:
We are aware that the other approach offers much more flexibility when it comes to design but we strive for the best possible user experience and thus we decided to use the non-app approach which is much more practical to use and fully supported.
Should Apple ever add support for true, native, developer-built watchfaces, we will be sure to make the most of that opportunity.
In the meantime, check out what we've been able to do at www.Lignite.io/apple.