Am I super late to the party in noticing this?
If this isn't a well-known thing that I'm just cluing in on now... check the artwork on p. 254 and 255 of the early access rules. Take a look at the people in line for the Helfyre show behind Rockstar - it's the cast of Vox Machina and the Mighty Nein.
Very in keeping with the spirit of Sentinels, what with cameos from Team Fortress 2, Penny Arcade and elsewhere appearing in the card game. Now I wonder what other cameos are in the book art that I haven't noticed yet...