Love & Support This:

Not sure why so many people seem to be on the fence/against it. WoW & FFXI both have these features, but it seems like its a new concept or something lol...

WoW:
Paladin, Monk = Heal, DPS, Tank
Rogue = Pure DPS (still had different trees to customize play style)
Shaman, Priest = DPS, Heals
etc...

FFXI: (Sub-Job System)
This stuck more to the main theme of triad (tank,dps,heals) but still offered huge gear/merit point options to build your character how you saw fit

Ninja = Were numerous evasion builds and was a tank for a lot of content, then switch your gear to STR/Acc stats and now I am a viable DPS
Red Mage = So many builds arose around this class and became well known for solo capability
Paladin = While this did hold true to being a Tank, you could still put on your DPS gear with a giant broadsword and go kill things if you choose to do so, you had those options available

Note: Even classes such as ROG/NIN that are obviously stuck in a DPS role could have weapon choices down the road just as one example.

Example: I would like the option to chose between different weapons:

Swords = Low Attack Speed, Higher Damage
Katana's = Medium Attack Speed, Lower Damage
Daggers = High Attack Speed, Very Low Damage

If I like to see bigger damage numbers I will choose swords. If I prefer a high attack speed style of play I will choose katana or daggers. This is just one small example of something plausible in the future.

I myself am one who looks up the most efficient builds and plays that build for the relevant content (dungeons/raids). Do I still want the option to have a different gear set for soloing or random goofing around? HELL YA!

I think the biggest issue with these changes is that the game is still so very young and often times I think that is forgotten. It will take years before this game is polished. WoW & FFXI have had such a long time to grow and improve and I think we will be playing a very different FF14 5 years from now.