Blood elves are not fell elves, it's a common mistake people make. The most they had some fel radiation, they never went all the way. Fel elves are like the felborne or these actual fell elves from the Sunwell raid to be precise.
Nah light elves is just a name that went it's own life on sites like these, also the place were they were first called like this(I know it's those light elves with brown skin from some other game). I like the name blood elf, I hope the name stays if that ever becomes some topic. The sunwell is what made it so and appearntly not every blood elf is infused with it according to what we see ingame. Hell, they even forgot about the whole cleansing, since golden eyes which was an appearent reaction of it, was only given to blood elves in bfa, the cleansing was in 2007, suddenly calling them differently doesn't make much sense and neither is a subrace of them.
I don't think we would need further diving in that sense, both groups you namecalled already excist and they have their costumization options already available, its more flavour of elves we already have and since one of them is available on both sides it should probably stay like this, since it already was the best outcome to the whole high elf debate that went on a little to long. It's already a huge favor, since they were literally playable since 2007, so there you go.