Assuming you actually enjoy playing retail, currently BFA 8.2 , how will you manage playing classic when it launches?
The launch of classic will likely coincide with a lull in retail, before 8.3 is released, which will be good for players wanting to try out classic. However 8.3 will eventually release and there will be new content to clear and another expansion coming up, the time will come when you will have to ask yourself 'which game do I want to progress in?'
With the time commitment that classic will take to progress at a decent pace, it doesn't seem likely that that will leave much time for retail?
How do you plan to manage your playtime if you want to play both classic and retail? Are you going to alternate each time you play, focus on just classic until you clear it and go back to retail, or just play classic on Sunday mornings as a break from mythic+, raiding, and WQs?