Who is Joana? Joana, (AKA Mancow, or FuriousPaul) speedran 1-60 vanilla WoW from 2005 - 2007. I have been server first to level 60 seven times in a row, along with winning Blizzard's "First to level 50" contest they held back in 2006. I also have the fastest time through original vanilla 1-60 WoW in 4 days 20 hours. I have produced a very useful 1-60 horde speed leveling guide along with a 1-60 speedrun video.
When it comes to Classic, Blizzard's goal is to provide an authentic Vanilla experience, but they also needed to come up with technology to handle many players at launch, which is similar to sharding. While the use of this technology will be limited to the first month following launch, many players are questioning this decision and wouldn't like to see layering in the game at all.
Keep in mind that these quests are optional, and are not necessary to continue leveling and capturing companions. They are also account-wide, so if you complete the quest chain on one character, you will not be able to complete it again on another. However, any progress that you've made will be saved and you can pick up where you left off in the quest chain on another character. The dailies that you've unlocked will also be accessible by all your toons.
In player vs. player designated zones, you will still be viewable and attackable by players, but you are not left completely defenseless. While engaged in a Pet Battle, any attack from another player will break you out of the battle. You will receive a 3 second damage shield that will absorb 50% of incoming attacks. The same exact wild pet that you were previously battling will respawn after you come out of combat with the other player. However, if you defeated the primary pet in battle prior to leaving the match, the pet and its team will not respawn.
1 All expansion guides are written in the Battle for Azeroth beta in order to have them ready on launch day. It's important to note that betas can be buggy and unstable and may delay and even halt our progress on the guides. Furthermore, the time between the start of beta and the announced release of Battle for Azeroth is much shorter (by about 2-3 months) than past betas. As a result, our primary focus is to have the Leveling guides updated by the launch, and only if those are complete and time remains will we work on updating the remaining guides. All guides not finished in beta will be updated post launch. You can read more about this here.
Occasionally it's also been proposed to re-randomize all the gear. We didn't have best in slot lists back then. People weren't starting out as a fresh level 1 character with a complete list of which dungeons to run at 60 in order to gear as quickly and efficiently as possible. Now, all that data is available. If gear were re-randomized then all of those lists would become useless and thing would be close to how they were. Which is a more important part of the "vanilla experience?" the fact that item X from boss Y has exactly Z stats on it, or the voyage of discovery? Personally I think that voyage is way more important. Do you remember how many points of which stat on the ring or whatever that Darkmaster Gandling drops? I don't. Would it kill your experience if the BiS for every class were in a different dungeon so people had to actually play to figure it out rather than simply consult a spreadsheet? I don't think it would. For that matter, it probably wouldn't be a bad idea to handle it intelligently so that the better gear is in later dungeons. I remember there because some weird cases where level 40ish gear was better than anything that dropped in level 60 dungeons.