It is too early to call in terms of maintainability, but I think that https://github.com/de-souza/hugo-flex or https://themes.gohugo.io/hugo-flex/ is a great theme to start your project from. And when theme is so simple, you have a good chance it will get maintained 
Its 100 speed score on PageSpeed is impressive.
I am considering of using it as a base to replace my current theme (I don’t use many features from it) and it generates errors.