Having a semi-aquatic race is a great idea, as long as their ability to swim/breathe underwater is limited. Even if they're handicapped on land, it would complicate things, as we'd effectively need a whole new set of rules to apply to these creatures.
However, as long as they're somewhat restricted, I'm all for the Luscervans.
One thing we need to take in to account with these races is that they need to appeal to the players. It's no good creating a new creature that no-one will want to play as, so we'll either need to give each race an advantage in the EoFFworld, or make them 'cool' enough to attract people into playing as them. The Ingmarians and Luscervans seem to fit the bill, but it's something to bear in mind for any other creations.
