I did some testing on the PTR today by myself and to me it seemed like Wintergrasp functioned exactly like it did 2-3 years ago on a diffrent Trinity Core private server. When I tried it on the diffrent server, it was more or less on the same level as Strand of the Ancient is here. It is playable and contains the basics of the BG, like siegeing gates and capturing the Wintergrasp Fortress. It does have minor flaws, however those flaws will never be corrected when there are nobody to test and give feedback. As there is no way you will manage to get the needed ammount of players for a proper WG on the PTR, I would suggest testing on the live server. Ideally two Battles for Wintergrasp a week. One for Horde to siege and one for Alliance to siege.
I did see that opening Wintergrasp was rejected a year ago, however as this is mostly intended for testing, I was hoping to not get the same rejection message.
Content related suggestions are not valid, content is often deemed to be released once it's ready to be released. There's no point suggesting X or Y content to be released.
I recall that we did get the very same answer when we suggested this back on Bloodcraft 3+ years ago and I doubt Wintergrasp will ever be ready if we don't go for an approach like this.
Please do share your ideas on this!