As necroaqua shared, we won't know for sure, as while there's no template system currently on the PTR, there were dev quotes (though a few weeks ago or longer) which shared that they planned to keep some form of a template system.
As for when a template system will come around? While there's no official word, in the past the devs seemed to prioritize tuning the numbers for endgame first before adjusting the template systems for PvP, as the template system on live and in the past in Legion were partially based on those tunings, as the template system not only adjusted stats and disabled some things (trinkets/some on-use items/enchants/etc.) but also buffed or nerfed a selected set of abilities in instances PvP (like looking at live, ret paladin's execution sentence deals a lot more than templar's verdict outside instance PvP, but within instanced PvP with the template aura, its damage is nerfed by ~50% or so, making Execution Sentence's damage be on par with Templar's Verdict).
Such template buffs/nerfs we see on live in lower levels (imho), were a product of proxy-balance from the template system for endgame (at least that's my thought on why Execution Sentence was selectively nerfed (amongst many other abilities) not mentioned), while survival hunter's infamous Flanking Strike and Throwing Axes evaded such template nerfs throughout legion).
Summary for guess on when a template system will come around (assuming devs choose to keep a template system): somewhere after tuning classes and numbers for level 120.
Specifically, tuning for endgame (level 120) PvE, then tune (through template, if any may come) for endgame PvP, which is a extra tuning based on tuned PvE numbers.
