Events like dynamis don't work for a lot of people and were never fun for a lot of people. I hope they skip it this time around and learn something from other successful MMOs.
One of the biggest factors that kept driving me away from FFXI for a long time was the number of people you needed to get anything done. I had the time when I was 16 and playing EQ back in the day but I work full time now and don't have the time so it just becomes content I'll never see.
I wouldn't particularly care if they had a 64-man event as long as you could get similar quality gear from some other event (that only required 4-8) and they didn't sink so much time into 64-man content that it cost the rest of the game.
Hopefully they will learn from other MMOs though. If you look at the history of development for EQ (as an example) they really catered end game to a select few guilds for a long period of time which alienated anyone who wasn't in those guilds to a certain degree. You look at the paying customer base and there are far more people not in these guilds than in these guilds. The ones in those guilds may play the most but they aren't really the cash cow and many of them would even un-sub between expansions because they ran out of content (while the rest of the game population was still slogging through content progression that was 1-3+ expansions old).
I was a raid leader for a long time and participant in end game player organizations for a long time in various games. Huge man events were never my favorite. They always start super late. Either it doesn't really matter what you do or any moron can ruin it for everyone. It's hard to organize that many people. There is too much drama over everything from who is partied with who ("Ewwww don't put me with HER she's a horrible cleric! I want to be in the party with Whoever instead!") to who gets what drops and loot systems ("Soandso missed a raid 2 months ago and THEY are getting the BP drop?!", "This DKP system is so unfair!", etc).
I honestly don't see a redeeming quality in large-man events like that. The only ones that I ever had fun in were the keep defense / conquering RvR combat in DAoC (so it wasn't even PvE).