The way I would solve this problem is that all pvp t4 gear is avalible at pvp 10 first off. Second off is that just like the difference between t3.5 and t4 (both use relic 4s but one uses a lot more of them, namely t4)(this is aside from rare relic 3 and 4).
Basically stating to make t4 gear available without new pvp levels to grind; just make it so that pvp t4 gear cost more conquest trophies/campaign badges to get than pvp t3 gear. If there were to be pvp levels up to 15, no one would reach that or very few would have the interest to.