I think roles were the alignment of 4e: they only cause problems when they are misunderstood, but it is so, so easy to misunderstand them.
I thought power sources are the alignment of 4E. Ah well. Maybe Power Source is Lawful / Chaotic and Role is Good / Evil.
Anyway, I do think the roles were a good idea. After all, they were always in the game. It's like Newton pointing out gravity - everybody knows the apple falls down, but now someone described it in a formulaic way. Even if 5E goes out of its way to avoid roles, there will still be the mobile damage dealer, the frontline tank, the artillery in the back, the guy who buffs, the guy who heals.
What I would like to see in 5E is that the roles are less strictly defined. For example Defender doesn't necessarily mean mark, it could be some completely different mechanic. It's basicly what we've already seen in later 4E.
You could make a checklist of different role elements, and each build / skill tree / subclass has four or five elements from the whole list. Your role is where you have the most check marks.
(Incomplete) List of Role Elements
Striker
[ ] DPS
[ ] Nova Spike Damage
[ ] Attack on Range
[ ] Mobility
[ ] Dodge / Riposte / Evasion
[ ] Stealth
Defender
[ ] High AC / NADs
[ ] Lots of HP
[ ] Shake off conditions
[ ] Punish attack on ally
[ ] Frontline control / block movement
[ ] Self-healing / temp hp
Leader
[ ] Buff attack
[ ] Buff defense
[ ] Extra attack
[ ] Move / reposition
[ ] Heal
[ ] Remove condition
Controller
[ ] Debuff / prevent attack
[ ] Lower defense
[ ] Immobilize / Slow
[ ] Terrain effects
[ ] Summon ally
[ ] Area damage
You can do this for any character in any RPG / skirmish game. It's not limited to 4E, or D&D.
For example, Slayer Fighters are [X] DPS, [X] Mobility, [X] High AC / NADs, [X] Lots of HP, which makes them Strikers who can stand in as Defenders.
3E Druids check almost everything, that's why they are called CODzilla.