If you play at 60 and don’t have the time to raid you’ll be seriously outgeared in PvP. If you play under 60, you’ll be at the mercy of people who have a lot of gold buying and grinding twink gear who can’t play the game at 60 and would prefer to stomp you with a number of abilities that they can effectively mouse click with.
Vanilla PvP is harsh. You won’t get rewards for being good at it like you can now with Arenas and catchup gear, and you won’t get rewards for doing it at your own pace, because the system is designed to reward people who commit more time to it to get more HKs.
One thing you could do is pick a broken class. We already have tons of data to theorycraft with, and we know that we’re not getting any balancing, so you’ll be permanently stuck with a built in advantage to help you equalize against players with more time than you.