At present, we have limited information about the future of PvP in 6.x. I feel as though my concerns won't be addressed or truly confirmed until the day of 6.0's patch, as they are fairly nuanced. I find these points important all the same.
To start, make sure you've seen this Lodestone thread for a collection of what we do know. So let's get down to it.
The Abolition of the Feast
We know that the possibility of Feast closing down or being removed is high, but I find it very likely that Feast will remain the only mode centered purely on the 4v4 team deathmatch format.
I agree that the public duties should be closed down to focus on the new mode, but I would highly recommend keeping Custom Matches open. I would even recommend allowing undersized parties to enter. I do not completely agree with the notion of basically deleting content. We already lost the Fold, Slaughter, and Astrologos. Please do not remove all avenues of playing the Feast.
Custom Matches in General
Please allow customs games off the hop with the new mode. These are absolutely instrumental in facilitating community-driven events and players wanting to compete at a higher level in general. It also allows people to test, learn, and help others develop as players. It's good for your community and will immediately foster a more positive environment.
Queuing in the New Mode
Square Enix has a habit of restricting you from queuing up in groups. I sincerely fear that they will implement some sort of forced solo queue into this new mode which will kill a ton of interest in it right from the start. Friends of similar goals and interests should not be kept from playing together.
The concern always seems to be toxicity coming from premades when the reality is there is a lot of toxicity that comes from the day-to-day tome farmers that start every match saying "time to lose!"
I expect contestation for this point, so rather than write an essay on it right now, I will gladly counter-point as we go.
I may continue to add or adjust points as information is released. Kindly discuss.