Mark-Kashman said, in reply to a comment from @ivan unger, that 'we are looking at how we can enable admins to be able to create new hub sites, and uplevel an existing site with the additioinal 'hub' capabilities.'
We are right on the cusp of re-creating our existing, multi-subsite-based, intranet with the new communication site-based design, using multiple sites with lots of pages instead of sub-sites. It will be really useful to know soon if we will be able to 'convert' an existing comms site to a hub site.
Otherwise, we will have to create a temporary site with links to the other related comms sites, then delete that and re-create the new site (with the same content) when the hub site option is made available.
Knowing if we will be able to make our 'intranet landing' page the hub site retrospectively ('uplevel') now will save us (and maybe many others) a lot of time and hassle later on having to re-create a new top level site with possibly a different URL (we have over 8,000 staff so I'm conscious of the need not to make too many URL changes). Our comms team want this to happen soon so it would be good if comms sites can be make a hub site retrospectively. Thanks