Removing classes would just homogenize the game for everyone but the roleplayer community and would very likely make it extremely boring to anyone trying to play at the top end. I know the common response to this will likely be "Well so what? That's only a small part of the community and we shouldn't be trying to appease them". Keep in mind though, it's the top end players who test and find the bugs (that get ignored usually), and who figure out how skills and items work and they're the top streamers. We do it because we benefit the most from having the game work at peak performance. Disregard that part of the community and you remove any incentives the company has to fix combat bugs or balance issues. The game has to remain interesting enough to keep the attention of all communities, from the lvl 3 in prisoners rags fumbling around in starter zones, to housing fanatics, to crafters, to roleplayers, pvpers, and all the way up to the competitive pve sweats.
Generally I look at what people choose between DD Healer and Tank...and guess what? DDs are an extreme majority.
Many have multiple characters and they build an Healer or a Tank just to get through parties, have you tried queueing recently as single DD?
It's like 20minutes for a base game dungeon.
Now, what does that mean?
People always choose the easiest option, punching things rather than managing groups and, in my opinion, that translates in a classless world as well...people just going to the easiest build.
Of course, there would be role players, casual players, weekend players, which would be happily crossclassing here and there but, at the end, the most important player base is the one made by active, so called "hardcore" players.
Those who make a build, try skills, check their dps and try to raise their bar of awesomeness and...hold tight...that's not wrong at all.
I mean, the game is made by mechanics and if you want to roleplay you seriously don't need them, if you want to casual play you will never reach a point of competitiveness where you even realize the class differences...probably you're just badly geared or simply not capable of playing and you blame the classes for your unsuccess.
As already been said the game is quite class related mainly for party buffs and support, each class has unique skills that help everyone around them and they all need to cooperate to go through the hardest challenges.
Casual players don't even realize that for bigger vet trials you need to organize classes and sets, knowing which class every player is and what they are wearing.
If you take that out what will happen?
Everybody would go for the awesome solo playable dps/selfhealing awesomeness build, not giving a single damn about being part of a party (lol, I like this sentence) and bye bye not only diversity but possibility of properly doing high level content.
Am I sure about this?
Well, as I said, try queueing as DD for a dungeon...you can't find 3 more people in 20 minutesnow imagine all that without class restrictions.