Uhmm....vote for a king? I believe there is a requirement of noble bloodline. Kingdoms are normally inherited or taken. Just my 2 cents. I do believe Casca has bloodline claim though, so it will be interesting to see if he will be allowed to rule.
Lord Casca of Heartwood wouldn't have needed such noble parentage to be elected monarch by the Royal Britannian Council. Atleast, that is based on prior precedent.
Lord Cantabrigan British, called the Champion of the White Light amongst Akalabethans (Ultima 0), posessed neither noble bloodline or birthright. He could not trace his lineage back to King Wolfgang or the Akalabethan Kings of Old; instead being a visitor accidentally displaced from earth (like the Avatar). Mondain, being the second son of King Wolfgang, had much more claim to the throne than British (You know, that could be an interesting claim if someone were willing to roleplay that). British became king by proving his worth (initially thwarting Mondains plans; but only banishing him from the realm of Akalabeth to return in Ultima 1). In a sense, Lord British is much like what some historians belive to be the historical King Arthur; a warlord who unites the Bretonnian Tribes and repells the invaders (Saxons).
In addition, I am not sure that royal lineage would've been necessary; even if there had been precedent of hereditary Kings (as there was in Akalabeth). The elves of Ultima Online are presented as an exceptionally powerful race of mystical beings; almost greater than the average human, much more like the elves of Tolkien than the elves of Greenwood and Gygax.