Yep, I think airlines will be putting in a lot of capacity to Europe next summer. For example, I think the remaining SFO-Europe (AMS, CDG, ZRH, and DUB) routes will relaunch in NW21 or NS22. A couple of questions regarding the rest of the international network:
1) Do you think we will see any additional LAX or DEN-Europe flights like LAX-FRA or DEN-CDG? LAX and DEN are not big Europe stations but with most TPAC destinations remaining closed, maybe we will see some expansion from those United States hubs.
2) Will United move ahead with launching the seasonal Intl stuff they announced in Fall 2019 that were supposed to start in NS20 but never launched (due to the COVID virus) like EWR-PMO/NCE? I do think UA will launch ORD-ZRH given that ZRH is a partner hub.
3) How are EWR-JNB and IAD-ACC doing? If the most recent launches are doing well, the next Africa routes I see 'em launching could include IAD-CPT/JNB or EWR-CMN.
4) Is the airport in the Maldives (MLE) big enough to support widebodies. If so, do you think SFO/EWR-MLE could be feasible?
I agree with your points considering SFO. I also have to wonder if they will add other markets not necessarily in Europe. Perhaps 2022 could be the year we see SFO-LIM/BOG? Those are sizeable unserved markets and as JayUnited said, South America may be ripe for a big capacity boost.
If we're talking Europe, and United is not afraid to consider lower-yielding markets, there are some key missing pieces from SFO that I'm sure would do well seasonally, namely SFO-MAD/FCO/BCN. MAD has historically been served directly by thrice-weekly IB A332 service, but the route is not bookable for 2022 and I personally believe it's been dropped. FCO is another big one that had been served by Norwegian from OAK. Norwegian was due to continue serving it after they made the switch to SFO, but of course, they collapsed before they could fly SFO-FCO. Alitalia even announced FCO-SFO for summer 2020, of course, before COVID killed everything. Had the pandemic not happened, SFO would have had not one, but two routes to Italy (MXP/FCO) and three carriers between those two routes, which I find astounding. Finally, there's BCN, which is served directly by IB for LEVEL, IAG's long-haul low-cost carrier. I doubt UA wants to compete with that, but SFO-BCN is *very* popular in the summer, with 2 carriers serving it in 2019. Then there's also VIE but personally I believe that OS, rather than UA, would be the one to launch that. A wildcard would be SFO-KEF, but I don't think that would ever happen on UA. Iceair cut it since it required a 19-hour stay on the ground at SFO in order to optimize the flight to arrive before the European bank so they could sell connections, not just O&D.
If UA is not afraid to chase lower-yielding pax, then these are some prime options that come to mind, at least from SFO. Other than that, I think ORD/EWR/IAD will totally explode with TATL traffic + new routes in summer 2022. Should be very fun to see!
+ your point about the Maldives – frankly they are way, way too far to justify direct commercial service. EWR-MLE is ~25 nmi farther than SFO-BLR, for context. And SFO-MLE is well over 8000 nmi. I have no doubt in saying that those two won't happen. Plus, they are the ME3's bread-and-butter and they would always beat UA on pricing.