The whole United B788 and B789 fleet is moving to three class as the Polaris refits are done. Deliveries from N29975 onwards came with Polaris, new livery and Premium Economy. The last 8 B787-10s are coming with Polaris and 3 classes and so the Dreamliner fleet will be fairly uniform. EDI is an A321 destination I suspect, not too long to wait.