I'd say making the generic/flexible "Elf" race would/should be the same as making just about any other race.
I have a framework..."template," I guess...that I use for races in my homebrew game setting/system. It should be simple enough to tweak for use in 5e with the addition of some "weapon proficiencies."
RACE
Abilities: +1 to ability A and +1 to ability B. -2 to ability C. Racial [natural/without magic] maximums may be 1) 19 in A
and B or 2) A
or B, and [in all cases, natural/no-magic] 16 in C.
Size. Movement Rate.
Special/Non-human Senses: typically twilight or dark vision, but also such elements as a [ye olde] dwarf's Stonecraft abilities or gnomes being able to sense gemstones (I make that a reason for the big noses. Gnomes in my world can, literally, smell precious and semi-precious gemstones, even through rock to a certain distance).
Then 2 or 3 special features.
Special Feature 1: typically a "Resistance/Resilience" thing as far as 5e would be concerned, save bonus against something.
Special Feature 2: typically something movement related
Special Feature 3: typically something cultural.
Languages: typically (though not always) Racial tongue, Common, +1 other.
So, all together, the race has 4 or 5 traits. In the case of using it for 5e, I guess it would be 5 since we would make that cultural #3 the weapon proficiencies.
For "subraces" you'd just have to mix and match/swap out a feature or two to alter the racial flavor to what you want.
My homebrew PC [high] elves look something like this:
[Steeldragon's World of Orea, "High" elves for use as PCs...tweaked for 5e]
ELF
Abilities: +1 to Dexterity, +1 to Intelligence, -2 Constitution.
An elf can have a maximum natural ability score of 19 in both Dexterity
and Intelligence. They may not, naturally, have a Constitution greater than 16.
Size: Medium.
Mv. 30'
Elvin Senses:
- Superior Twilight Vision: You see in darkness as if dim light and dim light as if full light to a distance of 60'. If beneath moon or starlight you can discern color and detail out to a distance of 1 mile.
- Enhanced Awareness: Elves possess sight, hearing, and tactile senses far superior to humans. An elf adds +2 to all Perception and Search/Investigation rolls.
Fae Heritage: Elves are +4 to rolls to save against enchantment magics.
Sure-Footed: Once per day per level, [not how 5e works, I know. That's my system, you'd have to work out some other thing. "Once per Short rest" maybe?] your character can reroll a failed saving throw or ability check dependent on balance (Dexterity) or against effects or circumstances that would inhibit movement (deep snow, narrow ledges, the Entangle spell, etc...).
Starblood Ancestry (again, this is elves in my world): The Miralostae elf's immortal origins, however faded, still grant them the following benefits:
- You are immune to the paralyzing touch of ghouls.
- Elves can't be put to sleep by magical means.
- You are unhindered by natural temperatures from -10 to 110 F, magical heat or cold effects you normally.
Languages: Elfin, Common, Sylvan (in my system, + a maximum number of additional languages equal to your Int. modifier. These may be chosen at character creation or accumulated as you advance. Player's choice.)
For 5e, I suppose I would shift the no magic sleep to the Fae Heritage, as the PHB already has it and remove the other "Starblood" elements to use that slot for the sword and bow Weapon Proficiencies.
For wood elves, maybe, I swap out Common for "Woodland animals," make the reclusive Sylvan Elves learn Common separately. I think I'd remove the Fae Heritage or maybe just lessen it to a +2 (like my half-elves receive). Sure-footed stays, for sure. +1 Dex., +1 Con., 19 natural max's in both/either; -2 Int., 16 natural max.
That'd be it, I guess. Unless i wanted to switch the prof's to spears and bows, instead of swords.
If I want sea elves, instead of "Starblooded" I'd give them "Aquatic Anatomy" which would include water breathing and swim speed, maybe enhance their AC slightly (thick skin for depth pressures). Alter their senses (-Enhanced Awareness) to include some kind of underwater sonar, feel/sense currents and tides, direction sense thing.
And so on and so forth for whatever flavor of elf you want.