They are getting 50 aircraft, and I can't come up with anywhere near that number of routes where a premium heavy narrow body would fly. While I think this is a great aircraft, and in Y it will be better than anything in the UA fleet other than the 763, UA can't go up against widebodies in J/PE (and would have a problem doing so in Y against a decent plane like an A333neo, B763, A359 that offers reasonably sized seats) with a norrow body.

I can see a few business routes that UA might want to do on this bird, ORD-EDI, ORD-AMS , some of the routes from EWR (or ORD) and Scandinavia (CPH, ARN, etc), perhaps ORD-Stutgart, or EWR-Berlin, EWR-Lyon, but much of the routes I would think UA would want to serve would be less premium business heavy, routes from ORD/EWR/IAD to spain/portugal, middle European places like Vienna, Prague, or destinations in Italy.

I would also expect these planes to be used on IAH/SFO flights to central/upper south America, none of which is that premium heavy.