Well I went on another route with Aces to be the last Pokemon before the Mega and not the Aces be the Mega for multiple reasonsBesides, it is not necessary Aces to be the Megas
First of all the Aces we see on the Leaders page are outdated as many times have stated by many and Ame herself, Second I make Adrienn's Mega to be Altaria so I change the Ciel's Ace.
For Titania, Ame one some thread about that Gigantic Steelix left the suspicion that we will see it again with Titania (Weird indeed, many was asking why Titania when Sapphira was the one who controlled it last time) so maybe we have some Mega Gigantic Steelix? Even no Mega Aggron is even better as wall so why not?
And for Sapphira when we have Heather with Salamence it's almost 100% that she have Mega Salamence too
SO TL;DR = Pluralism