As a long time DC PvPer in PC/NA, I am part of quite of a few PvP guilds and have a number of friends who PvP. Most of my guildies and friends plan on switching to IC or BGs or PvE farming for the testing months. Some of them are entirely dropping the game for the upcoming patch.
Most of our builds won't work and the work needed to remake the builds to some viable levels is entirely not worth the hastle. Some classes are literally unplayable with core skills on cooldown. Still a number of us would have been happy to join in Cyro for the testing as many of us play for the social aspect and general fun playing with friends as such. But the issue is that there is no real incentive for us to play in a semi-unplayable Cyrodiil.
Double AP is meaningless for a lot of us as a good number of people are swimming in AP accumulated over the years. Yes, sure having double AP is nice and all but most of us feel it is not worth the pain.
Some real incentives like Cosmetic rewards, free tri-pots and rare sieges, unique pets or something like a token of appreciation for testing like some other games offer during live testing events is sorely needed. Plus something rewarding the player for playing different classes by having unique drops per character would also be great as otherwise it is looking to be a stamblade fest.
Basically what I am trying to say is that making the test feeling more like an enjoyable, social community goal type event like other games do is the probably the best way to ensure that the masses show up for the testing. Otherwise, some of us are worried that this testing phase may cause irreparable harm to the already fragmented and fast depleting PvP community.