Plusnet will never answer that question with a "yes" as they are very secretive about any business plans. Worse than GCHQ
I won't hold my breath if I was you. The trial is still a trial after many, many years and no sign of that changing.
BT plc have to maintain some product differences between their 3 consumer ISP brands (BT Retail, Plusnet and EE) with Plusnet the value brand to combat Sky and TalkTalk. So I can see very good reasons why the plc wouldn't want Plusnet to sell the higher speeds as that could take customers from their main brand.