Flight pathing changes ie( rachet to org not going to crossroads)
Getting rid 1% spell hit miss on spells when Max hit on casters
Give tanks actual threat on there abilities or stances ie warrior def stance giving 50% threat
Give more talents points like fillers can be every 10 levels gives 2 and at 60 you get 3
Every 5 levels gives you 2 also so ie 15,25,35
This is if we’re having like wrath type talent trees
Druids proc on hit effects, let them drink potions in form
Casters get mana regen during battle while casting or improve mana regen
Or make int worth more spell power or crit or mana
Add expertise to get dodge immune/ get rid of weapon skill/glancing blows
Remove all world buffs not needed
Remove dot/buff limit
Improvement to the honor system not hit rank 14 and done/ improve pvp gear each phase
Make spells cheaper, they’re a huge gold sink
Make professions actually give greens that are decent stated as you level so crafted gear 1-40 being somewhat useful
Remove and ban boosting ie (huge mob grind boost like mara 350 mob pulls) if you’re a 60 helping low level friends/guildies running thru lower dungeons not a issue
Add GDKPs back into game but if you’re caught buying gold your character is deleted but blizzard makes sure it’s bought gold
Bots will always be a thing they’re majority of blizzard revenue now so can’t help it 
Group finder added but you choose your dungeons and there’s nothing bonus added like a bag of gear or money/exp just you choose a dungeon like black fathom depths and when it finds a healer tank and DPS it forms the group and teleports you in but alot will feel like this will remove the dungeon forming experience so I’m fine it not being a thing
Have raids ID work like retail that you’re lock per boss not that instance
These are some ideas throwing out to make classic better in my and friends eyes to make classic a better experience