Wasn't the upgrade to HD supposed to happen last year, but got pushed back?
I recall comments along those lines: where it was believed that trails would switch to HD when trail production moved back in-house, from Red Bee. But trails remained in SD after that move. I believe that the existing playout contract stipulated that trails must be delivered in SD. That contract expires at the end of the year, so it's possible that trails could go HD in 2018.
I know that locally produced BBC NI trails have been in HD for some time. Presumably the same is the case for BBC Wales and BBC Scotland - can't recall?