sub-space creation on the fly

Since spaces are also tags, I find myself needing to create them on the fly quite frequently and having all these spaces/tags as root spaces clutters the organization.

As the subjects implies, would be useful to be able to create sub-spaces directly from the page. i.e. from a note's + sign or the brain icon. e.g.

click the brain icon -> +spaces -> space/sub_space/new_sub_space

to create new_sub_space