Thank you for developing WVUI and the new Vue.js search experience! As a MW user, I am very excited about WVUI and keep watching the progress.
I write this post to just remind you that OOUI supports multiple themes and even a custom theme can be applied. (T100896) Of course, I have read the OOUI migration guide and know that the developers of WVUI are now focusing on needed use cases first.
I think the theme feature of OOUI is non-famous and not well used. But I am a big fan of it. I don't expect themes are implemented in WVUI soon. I want the team responsible for this to add this to the end of their long to-do list and don't forget it.
Best Regards.