[quote=@Isotope]
In my experience allowing fantasy races in these sorts of things usually ends poorly, but that said if others really want different species I am willing to allow Human subspecies.  That is of course if the people who want them can describe how they have arisen and how they fit into the greater world.

If you wanted to you could make such a sub species with elf like traits, but the trademarks of elves like magic and immortality?  I'm going to have to say no to those.
[/quote]Magic is an obvious no and save for a few series immortality isn't taken literally with them.
I feel their trademarks are other qualities but basically I wrote this before:

[hider=Elves]According to the studies of Charles Dwarfwin from the last century, elves evolved from the prehistoric birds. They share a distant relation with the various Griffin species albeit just barely. The elves' distant ancestor was the Homo Auger aka "bird-man" but there are evidences pointing towards crossbreeding and the exact history of how the elves developed is shrouded in many mysteries. Regardless of the apparently different origins it turned out elves and humans can interbreed with each other, siring a half-elf. Albeit 9 out of 10 such pregnancies generally result in a miscarriage and may even threaten the mother's life.

In terms of physical characteristics, elves are generally tall and slenderly built, averaging at 6'4". Their bones are hollow which further reduces their average weight to around 90 lbs. They are fast and nimble compared to humans, further supported by their amazing sense of balance. Some studies attribute the latter to tiny organic gyroscopes but the research on elven physiology is somewhat inconclusive. Elves are also gifted with impressive senses, capable of matching or outperforming most animals. They can smell like a hunting dog, see with an eagle's eye and hearing almost rivaling bats. Elves have a slower metabolism and require less than half as much food compared to humans. Elves can also boast with a great immune system which might be partially responsible for their longevity. Elves can live for 300 years. In many aspects Elves could be seen as the "winners" in evolution. Yet all these advantages come at a cost. Elves are notably fragile when compared to humans. Their bones are designed to withstand strain in certain directions but they are weak and brittle from other angles. Young elves break a lot of bones and gradually learn to move with grace and precision to avoid such accidents. Their low weight also means that elves can generally carry only 40% as much as what a regular human could. Elves are also more sensitive to loud noises and find them uncomfortable. Similarly while the elven immune system is great, their frail body suffers heavily when they're exposed to something this system wasn't designed to handle. Poisons that effect elves are often also very lethal. Elves also have slightly different diet from humans which means they can't consume a few types of food a human could (on the other hand their digestive tracts can metabolize cellulose and they can pretty much eat grass for nutrition). Lastly, while long-lived, elves suffer from criminally low birth rates. They are considerably less fertile than humans and the number of miscarriages is also higher. Modern medicine is aiding the elves considerably but their birth rates are still nowhere near to humans'. Elves also require over twice as much time to grow up and only elves past the age of 30 are considered actual adults (equal to the development of a 13-14 years old human).[/hider]

I can tone this down or overall alter things to fit the setting better.
But generally the point is to introduce the elves more like a sci-fi does its aliens than like a wondrous magical race from an RPG book.