almost a year now DMing 5e for me, two to three times a month, and I honestly cannot see a need for any new classes, except maybe a better Psioniscist. Every class mentioned falls into a sub-class for me. 5E is well done in that respect. To be real, some mentioned class ideas could easily be added as 'Prestige' classes (Knight of Solamnia, Duelist, Blackguard, Palemaster, etc).
Simply put, I have wracked my brain to come up with new classes, and every time I get them fleshed out , I realize a few tweaks and they become archetypes (Elementalist, Kensai/Samurai/Ninja, Favored Soul)
Now, if only we could divert this energy and change the thread title to 'What new campaign settings would you like to see in 5e?'