So based on this
not only the long lived companions already speculated about could make a cameo, but also others who were less expected like Imoen, Mazzy, Dinheirin (minsc's witch) and even more weird, they don't look like they aged on the artwork but rather as if they're based on their BG2 appearance. Moreover, wasn't sarevok and the fir-something- red dragon supossed to be dead ?
Anyways, cool, at least someone is giving us a few crumbles of information to speculate about BG3 (yes, Larian, looking at you, do something).
