I'm not sold on the idea that Ilberd deliberately selected the Primal's form beyond wishing for "something like Bahamut, but worse". So, I disagree with the speculation that he's attempting to draw Domans into the fray.

That said, his false-flag operation was pretty clearly intended to set the GCs and Garlemand at odds. Even without the summoning, it had every appearance of being an assault on Garlean territory by the Eorzean Alliance.

I'm not 100% positive that Ilberd was trying to hammer home that non-beastmen can summon Primals, but after the spectacle it's likely going to be pretty hard for Garleans to deny. I'm looking forward to seeing what their reaction will be. I somehow doubt they'll call off their campaign of terror against the Beastmen.

I'd find it hilarious, in a schadenfreud kind of way, if they expanded the scope of their holocaust to include not only Beastmen, but ANYONE who is not a purebred Garlean. "The world will not be safe until anyone capable of manipulating Aether is dead and buried." Naturally, given that the vast bulk of their armies and conquered populous are not purebred Garleans, this step of their long-term plan wouldn't be invoked until they had a firm grip on the entire world. At that point, they could begin the purges.