The primary reason for this is that core has already made many obsolete through block options

I'm not sure that the addition of richer design tools will make block styles obsolete. I think those tools present an opportunity to create a more flexible environment in which styles can created and shared.

Such an environment could even result in an explosion in usefulness. Styles based on portable configuration files are to me a much more exciting prospect than those based on static css that is tied to a specific theme.