There are 3 things or a combination of them to consider before merging xp on and xp off queues
1.
It is still a mystery to me of why there is a minimum ilevel requirement to queue for LFR PvE, but there is no ilevel requirement to queue for an unrated PvP.
For a low ilevel character, unrated PvP is generally more difficult and unforgiving than LFR PvE.
spoiler
I am not asking levelers to contribute unsettling amount of time and effort to deck out in top gear and don the BiS enchants and gems. But I am firmly asking them to have a reasonable ilevel before they want to party with me, regardless whether it is a PvE or PvP instance.
If someone shows up into 10-19 bracket with missing gear pieces, or into 20-29 bracket wearing common gear, I know they are going to s@ck. And they know they are going to s@ck. But they still join. And noone knows why. Because they can? Or perhaps because PvP community is busy bickering with each other instead of adopting a hardline stance of PvE community: “Sorry, Link. I can’t party with you. Come back when you’re a little… mmmmm… geared!”
Source: Minimum ilevel to queue for Instanced PvP suggestion
2.
Basically a stats template option for an xp off character entering PvP Instance.
A template which would severely scale down xp off character’s gear and/or character stats while that xp off character remains inside a PvP Instance.
spoiler
If an xp off character queues up for PvP Instance, then a gear template is applied to an xp off character upon entering PvP Instance, scaling down xp off character’s gear to the specified minimum ilevel, and/or stats template is applied to an xp off character upon entering PvP Instance, scaling down character stats to a pre-determined minimum value available in the current PvP bracket they have entered.
This way an xp off character will have their gear advantage negated when they enter a PvP instance, and such xp off character will have to rely on their skill instead of gear to win.
If an xp off character wants to do an Instanced PvP with other xp off characters only, they can always queue for Wargames instead of PvP LFG finder. In Wargames, a gear/stats template will not be applied to an xp off character, and Wargame queues would be separated completely for those who do not want to compete with xp on levelers.
Source: Stats downscale template suggestion
3.
Basically for money bags who want to pay Blizzard to enter the xp on battlegrounds as an xp off character, pay-per-bg.
PvP carrying happens in games like LoL wide and often, and even WoW arena carries offer the similar price per win with an in-game gold currency. Why can’t we pay Blizzard instead? I’d love paying up a reasonably consistent currency amounts to be able to go: “I am my carry. My destiny is my own.”