Perhaps a Customization > Theme component with a toggle on/off in the About page? I agree version numbers should be omitted. Options could also contain type. I would simply put
Powered by (Discourse bubble symbol) as a clickable image link to Discourse Meta.
Hence my suggestion above. As it would make it easy for a site to choose.
Version numbers is definitely something to avoid. The forum I volunteer admin on(didn’t have this level of access to maintain back then. Was originally a vanilla install with Categories changed/added. I don’t think they had ever ran the update in the ui or server root until I encouraged them to update the forum software as I was a full moderator at the time.
A member did use inspect to find the version number and used exploits to view a hidden group secured category. It was a closed beta so the leak did cause some dissension among the participants. It was handled. This particular scenario should be rarer as imho it was there inexperience with web ap maintenance that seemed to be the root.
Imho as long as the Team keeps the displayed "Powered by’ optional it should be fine.
@jidanni imho it should be the choice to display or not via a setting or optional component. As Discourse Instances can look very different due to it’s extensible design. While ppl like us might have an interest in this kind of ‘geek bling’. Most will be more interested in content and the ease of use. Most of us geek minded ppl know how to peek. 
