I can't find a single source confirming new Egis to appear in the expansion.

[Niqote]

"Leviathan, hmm... I'm not sure whether Ramuh or Leviathan will come first (laughs). I think it'll happen when the level cap is raised, so I really can't say yet."

"As mentioned previously, new egi will be added after a level cap increase, and we'll be sure to provide more details when that time comes!"

They are good comments, but I really think the bolded should be focused on ^^

From the letter, there is no talk of new Egis, but a mention of perhaps changing what the Egis look like (Swapping the skins, not the abilities)

I would like it very much if I could use Carbuncle as a full powered SMN so I am looking forward to how it might develop.

From Averex's link above:

During development, we thought long and hard about this, but we will not be adding new egi at this time. Looking at the long-term, instead of adding more pets, we felt it better to give more use to the job by adding actions to summoner. However, I’m sure many are wondering if they will have to continue looking at the same egi forever, but we are planning to add a system in the future that will allow you to change the appearance of your egis, including Carbuncle, but their stats will remain the same.