As far as I can tell, comment shortcuts have been around since basically forever.
The [tour] link got added sometime soon before June 6, 2014 (officially confirmed on June 11†), a short while after our About page instead became a Tour, and references to it got renamed accordingly over the next few months. Before then, however, we used [about] to ...
The comment formatting section of the editing help pages lists all the available shortcut links you can use in comments, including [help] for the help center. As of posting that is:
[meta] – link to the current site's Meta; link text is the site name
(e.g. "Super User Meta"). Does nothing if the site doesn't have (or
already is) a Meta site.
Magic links are hardcoded into the site software itself and as a result are network-wide, not per-site, so although technically possible in theory, the likelihood that Staff would add a magic link to every SE in the network that leads to RPG.se's meta about RPG forum alternatives is unsurprisingly very low. ;)
Although, as SSD explained, network-wide changes for an RPG.SE-specific code won't happen, there's still a labour-saving work-around available: add a premade comment with the forums link to the auto-comment script.
Based on our current roadmap, this isn't work that we will take on, as it doesn't coincide with functional areas that we plan to improve in the near future. We recognize that there's community support for this, but unfortunately, we can't prioritize it at this time.