Derplander's appearence has changed in ShB though - that appearence matches his scruffy, worn-down, 'dad-bearded' look in the ShB opening movie, whereas Ardbert still retains Derplander's WAR appearence from the 'End of an Era'/'New Beginning' ARR trailers.
As for Ardbert and Derplander's appearences in the logo are probably alluding more to the revelations someone or something is getting around in his physical body (remember, his deceased physical body remained on the First when he travelled to the Source under Elidibus's manipulation), and Derplander there is pretty obvious as he's the standin for the player's character. ShB made it pretty clear that the player character's original Amaurotine identity was the mysterious dissenting 14th member of the Convocation who is a completely different person to Elidibus - they're two totally different characters. So Elidibus appearing in the centre merely shows he's taking 'centre stage' in this patch so to speak (I agree though that the one getting around in Ardbert's meatsuit is probably Elidibus, but we'll find out soon enough anyway).
I'm not really sure that is actually meant to be the end of the original Star, as it looks far more closer to Dalamud, specifically moments after one of the 'keys' burst out and impacted with the ground explosively leaving a gaint hole in it, with Bahamut bursting free moments later- it has the same spikes sticking out, the ringed 'tron lines', even the same big glowing hole in it. Why Dalamud would be included in that logo... is anyone's guess... but if it is Dalamud, would be enough to create tinfoil theories aplently alone.
I couldn't find a specific image of the scene in question, but it's at this point in the 'End of an Era' trailer. This image is close, but it's taken before the Key dislodged and left the glowing hole at the bottom of Dalamud (but you can see where it is, it's the section glowing aetheric blue and violet near the bottom).
It also matches very closely to the artwork of the old FFXIV Legacy Campaign logo as well, but I think that's just coincidence....