To put more attention to icon themes that are available at the extension website, a new item at the bottom of the icon style list in the Options > View dialog should be added.
Example design of the list:
Get more icon styles online...
Clicking at this last item should open a new category for icon themes at https://extensions.libreoffice.org/extensions in the default OS browser (if possible/available in the same language as the LO UI).
I think an link to the extension webpage in the ui file would be easy to add and to the same job.
While this might be an option that is easy to implement I prefer the tighter integration described in https://design.blog.documentfoundation.org/2016/11/11/additions-to-libreoffice/
Not sure if this ticket is needed.
I would close this bug cause it's an generic bug as Heiko recommended in the linked blog post.