Roberty Rob

The actual rule is that the financial sponsor must establish domicile in the US no later than the immigrant's admission to the US.  For CR1/IR1 cases, the USC spouse is always the primary financial sponsor, so that rule applies.  While family reunification is all well and good, that's not the main reason for that rule.  The real reason is so the US government can enforce the terms of the I-864 affidavit of support from day 1, if it ever needs to.  That is, if the immigrant becomes a public charge, the federal government (or any state, local agency, or private entity that provides a means-tested public benefit) can sue the sponsor for reimbursement of expenses.  To be able to do that, the sponsor must be in the jurisdiction of any US federal or state court.
 
The requirement is actually in US immigration law.  From INA 213A, under "Determination of domicile" -- https://www.ecfr.gov/current/title-8/chapter-I/subchapter-B/part-213a
 
Under section 1183a: Requirements for sponsor's affidavit of support -- https://uscode.house.gov/view.xhtml?req=granuleid:USC-prelim-title8-section1183a&num=0&edition=prelim
 
The rule is also communicated to the public through the Department of State's website, in the I-864 FAQs and the DOS Foreign Affairs Manual --
https://travel.state.gov/content/travel/en/us-visas/immigrate/the-immigrant-visa-process/step-1-submit-a-petition/i-864-affidavit-faqs.html#aos23 9 FAM 601.14-7 re: Domicile -- https://fam.state.gov/fam/09FAM/09FAM060114.html  
Note that in any of the official sources above, there is no mention of family reunification.  Sorry to burst everyone's bubble 😆
 

Yes, filed online on 15 Apr using the USCIS portal.  Initially got an electronic message to say that the petition was being transferred to Nebraska for processing.  Receipt issued on 16 Apr from California.  Subsequently contacted the USCIS contact center who confirmed that it had gone to California for processing.  Expecting long wait.

Couple of things to consider but check these with the immigration lawyer first.  My USC wife filed the I-130 for me as the beneficiary online in Apr 21 and it is stuck at the California Service Centre.  We are moving to the US for a number of reasons, one of which is that her US employer has asked her to move back from the UK to the US.  We tried to expedite through USCIS last summer but our request to expedite was rejected without any formal response from USCIS.  We subsequently contacted her local (just outside Atlanta, GA) Representative and my wife completed a standard form (they get a lot of these) that was pushed through the Congressional USCIS Liaison Officer.  All we got back was a readout of why USCIS rejected the request to expedite.  The Congressional - Senator or Representative - route is worth trying, particularly if your lawyer suggests it.  However, to get something through USCIS quickly you will, as others have said, have to have a valid reason (in accordance with the USCIS manual) and evidence of it.
 
It may be worth looking at whether you have grounds to file direct with the London Consulate and submit a parallel I-130 through them. However, we took some advice from a senior Atlanta-based immigration attorney this week who basically told us to sit on our hands for a bit - the system is jammed up and will take time to un-jam. Her advice (contrary to some of what I have read on VJ) is that K3s are a non-starter.  Frustrating, but there it is!

Couple of things to consider but check these with the immigration lawyer first.  My USC wife filed the I-130 for me as the beneficiary online in Apr 21 and it is stuck at the California Service Centre.  We are moving to the US for a number of reasons, one of which is that her US employer has asked her to move back from the UK to the US.  We tried to expedite through USCIS last summer but our request to expedite was rejected without any formal response from USCIS.  We subsequently contacted her local (just outside Atlanta, GA) Representative and my wife completed a standard form (they get a lot of these) that was pushed through the Congressional USCIS Liaison Officer.  All we got back was a readout of why USCIS rejected the request to expedite.  The Congressional - Senator or Representative - route is worth trying, particularly if your lawyer suggests it.  However, to get something through USCIS quickly you will, as others have said, have to have a valid reason (in accordance with the USCIS manual) and evidence of it.
 
It may be worth looking at whether you have grounds to file direct with the London Consulate and submit a parallel I-130 through them. However, we took some advice from a senior Atlanta-based immigration attorney this week who basically told us to sit on our hands for a bit - the system is jammed up and will take time to un-jam. Her advice (contrary to some of what I have read on VJ) is that K3s are a non-starter.  Frustrating, but there it is!

We filed electronically in mid-Apr and had the familiar story of being notified electronically that the case had gone to Nebraska but with a receipt letter from California.  Eventually a call to USCIS confirmed California.  Tried to get it expedited due to a work relocation back home but with no success.  Since then I have been checking the USCIS account weekly and watching the data on this website.  After a couple of months where nobody on VJ being processed by California seemed to receive a NOA2 (maybe something to do with processing all the Afghans) it does look like things are moving again slowly.
 
My advice is to (a) make sure your timeline is correctly entered in VJ - the more data, the better the predictions and (b) watch how approvals on your service centre are playing out.  If you filter the data to show all cases (not just unapproved) arranged by NOA1 you can see how quickly things are being processed.  The official processing times are way longer than what seems to be reality for most applicants who upload their progress on VJ.  Finally, make sure that you are ready to go with either additional evidence for USCIS if requested or with everything that you need for NVC.
 
Hope that helps.