Blizz stated in a watercooler that they're using the 1.12 database as a starting point. I don't think it's a stretch for people to assume that most game features and mechanics will be in their 1.12 state. The kind of stuff I would expect to see reverted would be numerous AV changes, but I seriously doubt class mechanics are going to be reverted. I'd be surprised if the threat changes that ruin pre-naxx encounters are reverted.
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.
There’s the reason why some players used to call the game World of Roguecraft. Rogue was one of the most popular classes in classic WoW and there’s a good reason for it. During vanilla, Rogues topped DPS meters in raids and dungeons, but their main strength was world PvP. Rogues could stealth through enemies avoiding unwanted engagements with the opposing faction. Additionally, a huge variety of crowd control abilities and high burst damage made them the worst nightmare for the cloth-wearing classes. However, Rogues were in a bit of disadvantage regarding end-game gearing since most of their gear pieces were useful to other in-game classes as well.
The priest was considered the best overall healer in vanilla WoW. Priests had the biggest selection of healing and defensive spells which could be used in various different situations. Due to this fact, Priests had an easy time finding groups and guilds. If you’ll embark on leveling priest, expect some random whispers from other players inviting you to join their group as a healer. Shadow Priests were also considered as one of the best duelists in the game boasting with serious damage and healing.
World of Warcraft (also known as WoW) players have highly requested the classic version of their favourite game. As with any game, changes and major updates are added over the years. Since August 2006, many changes to the game have not been received well: such as trivialising levelling up. The level cap will drop from 120 to 60, but contrary to how that sounds, it will be a far more grindy journey of fun and progress. The current developers have made levelling up very fast in comparison to the classic days, purely to focus on end-game content and raiding which many people do not enjoy. Prior to these changes, many people enjoyed the games for years whilst not hitting max level, something never seen in the modern edition of World of Warcraft. The levelling process was a journey, having fun with professions and the grind that is no longer found. Of course, there are countless other changes that will be reverted, as you might expect when comparing something from 2006 to 2019.