Note: I did not read all 7 pages, I am replying to the OP.
I did a campaign once that were all humans landing in a world that had other races. It was a fun campaign that actually led to humans and kobolds being allies, but the players quickly got tired of it and wanted to add more races such as playing ogres.
When this failed because of the lack of diversity, my players wanted to try again with an all one race campaign, but wanted elven. This setting, which has been the main setting from 3.5+, started as an all elven group, which, oddly enough, turned into one of the elves turned lycan (werescorpion). This setting has been built entirely in game through players actions and back stories. What started as an all elven campaign, turned into a world where elves have an area, that is adjacent and allied with a very mixed area (mostly equal parts human and shifter (lycan, one in the same if they are civilized), with a splash of the other core races. These two areas also border a civilized goblin (civilized ones are call joblins) area. Within a few days travel is also a dwarven area, beyond that a halfling area, a dragonborn area (ruled by a bronze dragon), a savanna controlled by wemics, and even a learning, university area of githezerai. It became very diverse because the players wanted it.
My point is, what do your players want, and what are you willing to work with? My campaign that I wanted human centric, failed because the players didn't want to be human. They live every day in REAL life as humans. They didn't want to play make believe as a human. They were much happier playing fantasy races. The campaign setting we have created together has been far more satisfying that any setting in my 20 years of RPGs. Forgotten Realms? Yawn. Greyhawk? What? Dragonlance? Great books, boring setting. Playing in a world where your blacksmith isn't human or a drunk dwarf? Much better. You can go to a city and not be a minority as a minotaur? Now that's fantasy. Do what works for you, but I wouldn't have a successful campaign if we were playing Game of Thrones with D&D rules.
Also to note, none of the races are dying races, all races are building the realms. Humans aren't overtaking. Dwarves aren't secluding themselves. Elves aren't blocking their borders. Halflings aren't wanderers or hidden away into a shire. Minotaurs don't hide in caves. Centaurs don't live alone in the woods. Satyr have villages. Dragonborn have kingdoms. Dragons talk and can rule. Beholders are a real threat, not just some high level dungeon monster. At level one my players did encounter an ancient red dragon, rescued a goblin and worked for an adult bronze dragon while setting up the death of an old green dragon.