SMN is very good now, the only complaint is being stuck with the same three egis, we should be able to summon an egi version of each primal we have defeated.
Pet glamour could easily fix that however, just slot new egis into existing categories, making them an alternate skin of what we have now in order to make balancing easier.
Something like:
Caster Pet: Emerald Carby - Garuda Egi - Ramuh Egi
Tank Pet: Topaz Carby - Titan Egi - Shiva Egi- Bismarck Egi
Melee Pet: Ruby Carby - Ifrit Egi - Leviathan Egi - Ravana Egi
Lore wise it could be explained that we can't summon new egis because of our limited aether but a workaround would be found basically consisting in "replacing" those we have now with different ones.
With a system like this we could get an Egi at the same time a new primal releases, making things much more interesting.
I'll be very, very happy if this glamour system turns out to be something like this.