Nothing announced, it wouldn't be unusual for a trial within a month of the anniversary, but I think they may delay or skip the next trial because they know many players are waiting for it.
Zos watches forums for marketing strategy, the purpose of the ESO+ trial is to show it's benefits, if people already loudly desiring those benefits then it makes sense to wait and see if they will pay for them.
My prediction... Depends on how Blackwood companion progress will work when blackwood joins ESO+. If companions only level-up if you have access to blackwood they will do a free trial soon after high isle releases, to get people to try companions and want to purchase blackwood or high isle for more companion progress. If companions can level up after loosing access to blackwood the free trial may be just before high isle release.
#1 tip (Re)check your graphics settings periodically - especially resolution.