Actually we have allreaddy everyone but Druid from D2.
Amazon = DH
Paladin = Crusader
Barb = barb
Assassin = monk
Necro = wd
Sor = wiz
Druid = (no druid yet)
I don't agree with this TBH
Amazon javelin tree isn't represented at all in D3.
Paladin melee portion of the combat tree is more similar to Monk than anything else.
Assassin Trap and Martial Arts Tree isn't at all in the game, DH Caltrops, or Monk LTK etc aren't nearly the same IMHO.
WD have no bone skills or curses like Nercos did in D2 and although poison is a popular rune choice for certain WD abilities the said skills aren't similar to things like poison nova.
There are no druids but some of their signature spells have a D3 equivalent.
Armageddon = bombarment (Sader) or rain of vengence (DH)
Summon bear = Gargantuan (WD)
Summon Wolves = zombie dogs (WD)
Tornado = Tornado (wizard)
All in all I think the most unrepresented classes in D2 are javelin Amazon builds, Assassin Trap and Martial Arts trees, and both Summon and Bone necromancer builds. I think adding a class that just used javelins would limit build design options- same for a trap assassin type class. That said I think a Diablo 2 like necro class could bring back a lot of the fan favorite abilities like Teeth, Bone Spear or Spirit, Psn Nova. Curses for zDPS builds, hell even bone walls/prisons for collecting rift density.