If the possibility of flying in the old business class seat is too dangerous for a 3-month(+) advance purchase, then, obviously, the alternative is to fly another airline that better meets one's needs. Pretty straightforward.

I make this point merely to recall the dozens of other situations in the past where panic over aircraft swaps in advance schedules turned out to be much ado about nothing. Recall the concerns around this time last year, when the W18/19 schedule began to load, and a number of Polaris markets (including SFO-NRT) were initially showing old 772 cabins? Things change as schedules are finalized.

The HKG situation is clearly an unusual exogenous circumstance, not just the latest manifestation of United's ulterior motive to completely screw over every single passenger...

How in the world is going from 1x 78J and 1x 77W to 2x 77W from December 2019-March 2020 on EWR-TLV a response to AA DFW-TLV 789 3x weekly starting in September 2020?!?

Yes, I have been increasingly doing just that. Unfortunately, the CX options that were available when I bought the UA ticket are now considerably more expensive.

I'm pretty sure you don't mean to defend how UA juggles seat assignments when they switch back and forth between configurations (sometimes two or three times) in the week prior to departure.

Now we are talking about different things... my initial comment is that it doesn't make much sense to bemoan the loss of Polaris seating on SFO/EWR-HKG, as though it is all but assured, for an aircraft change (in a fleet actively under conversion) several months away.

Not really. Risk of multiple swaps is one of the consequences of UA not dedicating Polaris configuration to the route. And it's one of several reasons I'm less than thrilled about this change.

Let's wait and see...

Patience has never been a strong suit.

Just curious, did you end up cancelling? Or have you tried to call and rebook, citing the change in configuration?

There's not going to be a UA rebooking option that fits my plans. Depending on what I can book on CX or BR, I may cancel for refund, but not until after I've flown the outbound (HKG-SFO in October).

Changed my seat to 8D both ways. I like the window seats in Polaris a lot, but do not like them at all on the 772.

Did the same thing on my flight EWR-HKG in early Jan. Went from 8E to 9A back to 8D after the switches.

Rerouted EWR to HKG
 

Decided to travel on a different route.

Although I am upset my winter trip in March 2020 will not be true polaris now, I planned some MR in 9-across Y to HKG, gotta try to make the best of the situation...

I just don’t get how they don’t have to at least maintain the P+ configuration regardless of aircraft used. They made a big deal about EWR-HKG being a launch market and it will be done in like 6 months. Seasonal P+ is silly marketing .

There is a certain arrogance to pulling the P+ aircraft off a route after it's been marketed as P+ launch route. And then refusing (at least so far) to make any sort of reasonable accommodation for the pax who actually paid for P+.