...making a D&D game with something different in terms of classes and races, which very few of those games did.
— Some races to try out could be Warforged, Tortle, Tabaxi (everyone loves cats now), Shifter (several variants), Goliath, Dragonborn, Changeling, Firbolg, Loxodon, Kenku, Chitine etc. Most of these have never been in a game before, or just once. Races like the Chitine could add the interesting feature of "climb speed", which basically using walls as normal ground.
— Not too many new classes yet in 5th. Edition, but they could try adding the different Artificer variants, as well as psionics (I think so far just the Mystic came out).
Also with different expansions and DLCs new classes and races could be added.
Crossing fingers here.
I think there is very little likely hood for any race that is not in the PHB, VGTM, MTOF, Tortle Package or EEPG. Maybe the Verdan or Shifters, both are canon in the realms.