I'll preface this by saying that I'm generally against racial abilities.
However, I'd also say that if there was time and/or money, I'd love race specific costumes. To me, it sounds like the best kind of way to bring uniquity of race into the game without pushing people down a few limited and obvious routes if they are building a character for a specific playstyle and want to be as good as they can be at it.
I also think that if racial skills end up being a major feature it would be better to keep the number or races on the lower side, and not to have sub races (especially if there were a requirement for lots of special assets to be created for each race). The more different options you have, the exponentially more difficult it is to make sure that all your bonuses are roughly even. While it might seem interesting to have (just as an example) 4 element with 5 sub-races each, if only a couple of them ever get picked because they are clearly the best, I feel it would have been misspent effort.
That negativity aside, you idea about Lakemen who can wholly breath underwater has highlighted something that I hadn't ever really considered. My instant gut reaction was "That's silly, being able to permanently stay underwater is way to overpowered", but when I actually stopped to think about it, I realised I was comparing things on how games I've played in the past have been, and that I was being somewhat short sighted. Which led to a minor epiphany.
Instead of making racial abilities minor differences so that they are easily balanced or not be too impactful on your choice of race, why not go the other way and make them SO different that you can't actually compare them at all, and that they promote interesting or unique gameplay. Taking your Lakeman example, I think it could be really interesting to have a class that can breath for an unlimited duration underwater, but has an oxygen bar when not in water. The possibilities of literally having underwater cities, submerged cave systems and such are quite an exciting concept. Unfortunately, it is likely to be a little late in the development process to be throwing these things in. There would have to be scope for raising the sea level on maps to allow for truly deep oceans, it would have to be able to generate flooded caves and other aquatic landmarks. There would have to be enough content to make the underwater world as involved as the overwater world (not to mention working out what to do with the dynamics of fluids when you break into a cave with an air pocket from the ocean).
But all in all, that's the sort of thing that could actually make me a believer in racial traits. It's certainly something that would make a great expansion to Boundless.