In the same boat as the OP - UA1k segment flier primarily out of BOS/MHT and PWM with about 40% of my segments getting me to 1k under *A on US.
I'm guessing OP might be in similar boat as I am with the merger and will be easier to go all US/AA segments with the merger and loss of *A on US.
I emailed US to see if they'd go beyond the trial challenge being it's an opportunity for them to grab 100% of my revenue away from UA and got a phone call from US a few days later. She said they won't be offering anything other then the current trial for $200 that she's aware of anytime soon. My conclusion between the call and my research with limited AA flight options for me for an AA challenge even if it was avail is to go with the US Silver Trial for the $200 and will easily get in the segments for Platinum.
Phone agent said Chairmans level is not available under the trial but thought I saw something on website saying 40 segments in the trial gets Chairmans.
I would say with the phone call (which I received last Friday 1/3) is that US has no plans on killing the trial challenges.