Yes I did (I have a service dog, though but brought rescue dogs along as flight companion). No restrictions on long flights that I know of (yet). Nothing in the CoC as well.
If you can't get them to respond to requests on the phone or e-Mail run into any issues, the current
covid-19 travel waivers allow you to cancel tickets booked online without penalty.
Tip: Call the Seattle office directly rather than the 800 number (206-516-0300 for sales, or try 206-246-0755). No idea when or if that may be open. But it has to be if the flight is operating.
And don't forget to download, print and complete
this form
I don't know if you plan on flying business class, but their business cabin layout is perfect for flying with pet carriers. On the A350, A/K Window seats in the odd-numbered rows (1,3,5,7) have space for the carrier between the seat and the window where it is totally out of the way and very private.
If flying economy, I would normally recommend going for the extra-legroom "economy smartium" seats with a pet carrier (36" of legroom for an upcharge of $170, available only on the A350). However, if you plan on traveling in the near future, and with planes being as empty as last seen 18 years ago I think you'll be able to enjoy a whole empty row for yourself and there's no need for paying for premium seats.