Accordng to ISP Review, the official rollout is about to start:
"UPDATE 1st Feb 2018
We understand that so far the ECI Retransmission Trial has migrated around 600,000 lines and the official rollout is about to commence across their estate. The xdB (3dB profile) has also been successfully applied to some ECI lines."
It may still take some time though, depending on how many ECI lines there are and how many Openreach migrate daily.
Still sounds like very good news - and no, you wouldn't be able to change where on the upgrade schedule you are...