Unless Blizzard is disabling legendary affixes in PvP, even if Blizzard right now changed their philosophy on Covenant and let you swap freely, this still wouldn’t address your issue of wanting to be 100% optimal in raids and 100% optimal in PvP. By the time the raid and PvP season starts, you will only have had time to craft ONE legendary, and if those forms of content don’t have exactly the same BIS one form of content won’t have its legendary affix.
If you want to be most competitive in both raiding and PvP, you will already want to maintain two rogues so both your rogues will have the legendary they want.
It really matters what level of commitment you want to make to being competitive.