That's actually 4 slots (2 Each Way) for your scenario. Since LHR is not a * Hub, connections are less available than say at FRA or MUC . I'd speculate that a CLT-LHR flight would be less profitable than CLT-LGW and may not be justifiable because of the LHR slot purchase prices. There's likely a good reason for using a 333 year round on the current CLT-LGW route - possibly high cargo yields and/or business contracts. It's my understanding that CLT-LGW has been profitable for several years.
Consolidating a potentially loosing operation rarely leads to profitability.
Except that LHR IS a *A hub. Sure it's not the behemoth of a hub that FRA or MUC are, but BM does provide connections to secondary cities in the UK and Ireland which is more than what LGW can provide. CLT-LGW does fine but it needs to be shifted to CLT-LHR in the long term because that's where the premium traffic is headed to. Like you say though, US has likely determined that it is not worth the slot purchase until economic conditions improve.
The local CLT-LON traffic US carries isn't going to change much since the nonstop to LGW is still preferable to a connection elsewhere, but US is at a disadvantage for the business LON flow traffic since it serves LGW and not LHR (from markets that don't have service/suitable connections to PHL). Plus, there are savings that would result from closing the LGW station and consolidating operations in LHR.
IMO, adding a 2nd PHL-LHR flight would require a 2nd pod equipped 332 to compete with (and take business away from) BA and could prove to be a futile effort, wasting a valuable resource for a trial year. Competing for BA contracts requires a sustained effort to excel in quality and services - something US has not seemed willing to do on any route - except possibly for TLV. PHL-LHR using the 762 was supposidly not producing acceptable yields. Hopefully the podded 332 and improved onboard services has improved the situation.
Hmm, I'm surprised we actually disagree on this one considering it involves more international flights out of PHL. I believe that a second PHL-LHR flight is key to the overall success of the PHL-LHR route, and should be considered before CLT-LHR service is even though it likely won't be (see above, regarding savings of closing LGW). Both frequency and product, as you point out, are going to be important to winning corporate contracts on a route like PHL-LHR. While US improved its schedule slightly by moving up its eastbound flight by one hour, it still desperately needs an earlier eastbound flight that would leave PHL around 6pm, allowing business travelers to arrive in LHR at 6am and giving them an entire day to do business there (the current departure puts you in central LON around 11am at the earliest).
Actually, the whole Open Skies hoopla never really materialized (so far) into a gold mine for any carrier - other than possibly those who sold slots, such as BMI. In fact, CO has reverted to using 757s on 3 of their 4 EWR-LHR flights.
Yet you cast aside the fact that CO bought 5 pairs of slots for EWR-LHR flights (5th one starts this fall) in two separate transactions. Clearly, CO recognizes the need to be a player at LHR in the long-term.
But to get back on topic, I think there are much better uses for this plane than for CLT-HNL, if not immediately, certainly by the time next spring rolls around. It was good to see them give it a shot; I think year-round was a big mistake from the get go but clearly it performed poorly even in the high season. There is no reason to keep CLT-HNL around if it is unprofitable since US can still effectively serve the market via PHX. In fact even when flying from the east coast, it is less circuitous to go via PHX than via CLT.