I just finished forming the kingdom of Plunder Isle, and I was hoping to stay Murloc/Nerglish and form a merchant republic to take advantage of all those fertility bonuses and flood the market with trade posts. My capital is coastal (Starfall), I have legalism at 4, still waiting on trade practices and the city upgrades, but my current government type is tribal monarchy, and the decision to form a merchant republic is not showing up for me in the intrigue menu. I believe I've met all the vanilla requirements for a merchant republic, and the decision to adopt feudalism is there but greyed out, so where is the merchant republic option?

I even tried mass converting to a civilized religion (Scarlet Light) and it still didn't show up. Are Murlocs hard-coded to not be able to form republics?