I'm not even sure how they would have transitioned WoD's gearing system into legion given that the rest of the game rewards gear completely randomly and gear vendors with guaranteed item levels at current tier just doesn't fit with that. You'd also run into a bunch of dillemas involving secondaries and item levels, since you don't get to choose the secondaries on the gear that drops in world content or m+. So they'd likely have to make your current season's pvp gear set ilevel at current LFR level and make it scale to heroic level inside of instanced pvp or something (since you got to pick the best secondaries). But then you would have a set of gear that changes ilevel and then also a template that then changes your stats based on that ilevel, and you'd be even more gimped in world or pve content. I don't think any of that would increase incentive to pvp in the current environment. I think participation would be just as bad if not worse had they kept WoD's system.
Having gear that was only accessible at a certain rating was always the carrot on the stick for me to want to tryhard and increase rating back in bc, wotlk, and cata. I think the progressively increasing ilevel reward based on your rating solves that because you always have a potential upgrade and you know higher rating = better gear, but the follow through on the system just isn't there. For all of that to work, the item levels need to be on par with the rest of the current content or it's still just as irrelevant as before. Here's my best crack at an idea that attempts to bridge the gap between old and new systems to maybe get the best of both worlds:
What if prestige was seasonal and you received more honor per win the higher rated you were. Your available drops go up in ilevel as you increase prestige. Make the honor gains scale exponentially with rating such that you couldn't just spam a bunch of low level games and feasibly get super high ilevel.
Then, instead of having gear randomly drop for you, you have a currency that drops from wins and issued to you when you increase prestige rank. This currency could be a token that matches the little emblem thing that you already have for each prestige rank and each higher rank of this currency rewards you an upwardly scaling base ilevel piece of gear when you trade it in. You take this currency to a vendor who either gives you a piece of gear or a loot box with a piece of gear in it.
Maybe if they don't want it to be an exact trade (i.e. let you pick what piece of gear you want), you would get to pick from a loot box that has a weapon that costs x number of coins, a box that has a chest/legs/helm/gloves/shoulder that costs y number of coins, a box with belt/boots/bracers/back that costs z number of coins, or a box with neck/ring/trinket that costs the least number of coins. That way there's still some element of randomness, but you're not trading the same amount of currency for a weapon or chest that you'd be trading for a pair of bracers or a ring. They'd also need to make sure that the ilevel tiers per prestige rank are similar to the item level of gear you'd be getting from equivalent pve content.
Add on top of this the ability to get some kind of marginal yet non-negligible honor gain from a daily random bg, pvp world quest thing (bfa) suitable for your prestige level to incentivize mild participation in all of the other pvp content for players across the spectrum of skill/rating. Just my best crack at a go-forward idea that might be better but not exactly "earn points + trade points for gear".