Every class is core. If you don't think a class is unique and interesting enough that it deserves full support, improve it until it is.
That said, I think that 5E should be able to reproduce all 3E and 4E characters eventually, after enough splatbooks (there is some pretty wild stuff in late 3E though, like Incarnum). I would start with the 4E class list, but merge a few classes. Essentials has shown that with subclasses (I'd call them paths) you can have different builds that fill different roles. I also think that not every class needs to fit a role to a T, there can be mix and matching.
/ represents a role mix
, represents different builds
PHB
Fighter - Defender, Striker (Slayer), Leader (Warlord)
Rogue - ranged Striker, melee Striker
Bard - Leader/Controller
Druid - Leader/Controller
Wizard - Controller, Striker (all 8 schools of magic)
Cleric (in robes, using a holy symbol, Runepriest mechanics) - Leader
Paladin - Defender/Leader
Swordmage - Defender, Striker (Duskblade)
Barbarian - Striker, Defender (Warden)
Sorcerer - Striker/Controller
Ranger - ranged Striker, melee Striker
Later
Monk - Striker, Controller, Defender
Psion - Controller
Psychic Warrior - Defender, Striker (Soulknife, Lurk)
Cleric - Striker (Avenger), Controller (Invoker)
Druid - Defender (Shapechanger)
Warlock - Controller, Defender (Hexblade)
Ranger - Controller (Hunter, Seeker)
Wizard - Leader (White Mage)
Summoner - any (depending on summoned Bestia)
...