As I mentioned upthread, I don't think DEN-(LAX,SFO,IAH,ORD,IAD,EWR)-INTL, or the reverse, traffic is what UA wants utilizing a PL for a variety of reasons. Thus if most DEN-INTL traffic winds up on A -- which, given the structure of FIS at DEN appears to be essentially mandatory for arriving passengers and wouldn't take major gymnastics to accomplish for departing passengers putting it a PL on A makes sense. It also comes with the bonus subtle deterrent factor for those doing the DEN-connect-INTL routing off of B.

But to your CapEx/OpEx point, absent a major competitive threat, the likes of which I'm having a hard time imagining a plausible scenario [F9 adding lie-flat seats and offering NS service from DEN to Europe's capitals with their own "Ursa Lounge" product? BA setting up a hublet and offering more destinations outside of the UK?] unless and until UA has more premium cabin -- preferably consistently paid premium cabin -- lift nonstop out of DEN I think a PL in DEN is a ways off. One could argue, for example, that LAX's only major justification for a PL is to differentiate UA from competing intl carriers like QF, and if UA didn't have route overlap a PL would still be a long way off.

The pictures up-thread also tell a bit of a story -- if a PL were in any way eminent DEN would have just thrown up construction walls and left the space shelled. The presence of carpet, etc. suggests that this is not an eminent project, on the other hand the fact that there are no concessions, etc. generating revenue suggests a +/- 5 year plan and almost certainly less than a +/- 10 year plan IMO -- otherwise another tenant could build something out cheaply and justify the amortization of the capex knowing they'd be gone when their lease was up.