Limit the number of classes. When I see games announced that have 40+ classes, I cringe. It sounds cool, but there's just no way to make 40+ classes feel unique and special. Balancing those classes is also a gigantic nightmare. For my EQ3, there would be probably a small number of classes with a variant spec for each to add flavor to your primary job.
Warrior - tank or dps spec. You either take a beating, or you dish it out, but not both.
Paladin/Shadowknight - You're either a healing focused tank, or a disease/pestilence focused tank. As a hybrid, you are middle of the road at tank & heal/dps. Flexibility is your asset.
Wizard - Pure Arcane or Necromantic. You're the glass cannon (wizard), or you're DOTs and raised undead pets. Either way, you deal damage.
Healer - Cleric or Shaman. Cleric is magical based.. Shaman is natural based. You're really the same job, just with a different way of getting it done.
Physical Damage - Rogue, Ranger, Monk. Rogue relies upon stealth and position. Ranger is ranged damage specialist, up close you'll get smoked. Monk is the close quarters fist fighter.
I'm aware this list is missing some of people's favorite old classes from EQ, but I'm OK with that.. Start small, and add more classes later in the game maybe, but only maybe.
I largely agree with your vision with a couple of exceptions. For starters, I struggle to see a game that focuses on forced group interdependence yet does NOT have a crowd control role. CC is such a huge part of why players need to group. If there are no classes that specialize in CC, then I can't help but feel like it's largely a missing mechanic in your game, which is sad.
Also, giving only one class (War) the option to spec tank or DPS seems imbalancing to me. If it were me, I'd consolidate your Warr/Paly/SK classes by dropping the option to spec DPS and allow them to do their primary job (tanking) differently, the same way healers heal and DPS classes damage. Then create a CC role by way of a Bard or Enchanter. Everything else looks tight.
Yes, this class structure looks extremely familiar and I'm ok with that.
In terms of content and zone design, my vision would start with similar concepts to EQ1. Of course they need outdoor zones, cities, etc but places like Mistmoore, Unrest, Lower Guk, Karnors, Sebilis, Velks, are all great zones to pattern design after. I don't mean recreate those zones (although you could). I mean, use the same principles, such as sprawling and/or vertical layouts, dense mob pop, wanderers/roamers, rares/named mixed throughout, etc).
I'd also like to see some newer mechanics as well. Say what you want about it but I'm very intrigued by the disposition system being touted for Pantheon and would love to see something similar here. In short, mobs need better AI and that's a step in the right direction, IMO.
The last thing I'll touch on is with regards to itemization. I agree that today's games are incredibly bloated and that includes EQ Live. Entirely too many items and a ridiculously quick power curve have completely devalued the accomplishment of attaining anything. I still believe you can utilize today's spreadsheets/tools to design loot (in other words, it doesn't need to be hand-crafted) however, make loot fewer and further between instead of dropping like candy everywhere or given out freely as quest rewards. And take your time with the power curve. I'm fine with being in my teens before I get my first piece of magical gear. I just don't want to be lvl 40 and already equipping single pieces with +200 in all stats.
And the raid game should see an increase over group gear but not be so overly large that it creates an entirely different game between players (i.e. content that is challenging to groupers but raiders completely faceroll).
I could go on but that's enough for now.