For the record: The historical state of Swiss nationality law is set out in the Nationality Manual (downloadable in all Swiss languages, the French version is at
https://www.bfm.admin.ch/bfm/fr/home...rgerrecht.html with links on top line to other languages)
As early as 1957 certain Swiss women who had lost Swiss nationality could recover it. By 1991, responding rather belatedly to the 1979 UN Convention on the Elimination of All Forms of Discrimination Against Women, most such discrimination was abolished, though arguably not (yet) with total effect regarding prior multigenerational discrimination. See http://www.persee.fr/web/revues/home..._num_43_3_2291 (Michel Hotellier) and the texts of historical revisions at https://www.bfm.admin.ch/dam/data/bf...ueg-anh1-f.pdf (French version).
Article 9.1 ("La femme suisse perd la nationalité suisse en épousant un étranger, si elle acquiert la nationalité de son mari par le mariage ou l'a déjà et ne déclare pas lors de la publication ou de la célébration du mariage vouloir conserver la nationalité suisse.") was abrogated by LN du 23 mars 1990 (RO 1991 1034).
Many Swiss women retained their nationality even earlier (in the USA following the Cable Act of 1922) because automatic naturalisation of women upon marriage was progressively abolished; the trap for the unwary was applying for naturalisation without first consulting the relevant Swiss consulate. (Even today this issue is faced by German citizens, although as to those naturalised in the USA there is a perfect defense in the US estate tax discrimination against foreign spouses (the "QDOT" rules) -- that defense might perhaps have been of use to some Swiss brides as well in the past.)
There are several scholarly treatises on this subject. For a list, go to https://jus.swissbib.ch/ and query on and/or (somewhat less satisfactorily) As for marriage in the USA: It's about the easiest jurisdiction for marriage, with no query as to immigration status and generally self-certification as to civil status. Nevada is famous for quickie marriages; many or most states have a waiting period: thus, 72 hours in Texas which is why many spontaneous marriages take place instead in Texarkana, Arkansas, across the street from Texas. But watch out: at least one couple married on the Arkansas side (Miller County) with a license issued by the Bowie County, Texas clerk: http://uniset.ca/other/cs6/295SW2d330.html
Apparently the marriage certification document (not the marriage, only the date of the paper certification) has to be less than six months old when presented to the Swiss consular officer. (That's only a minor nuisance most times but I had a client who entered into a Jewish marriage in England, and synagogue marriage books aren't filed with the borough clerk until they are filled up -- which can take years, or decades in the case of Chelsea, London.)
American tax laws regarding expatriates and loss of citizenship/green-card status or long-term residence are draconian. Residents of Switzerland are likely to face issues more serious than finding a willing banker: PFIC, FBAR, and rules relating to trusts, foreign corporations, investments, and income (and for the wealthy, gift and estate) taxation. Long-term residents and green-card holders should seek tax advice when leaving the USA for good. (Apparently those nasty tax rules even apply to illegal aliens and deportees, if they have substantial assets.)
The OP seems to be going the other way, gaining US citizenship. I wonder how far the Surinder Singh strategy would work for him (immediate EEA residence visa in a neighbouring EU country provided the Swiss spouse seeks work there; with usual Schengen rules for brief visits to Switzerland. And after six months non-discretionary rights to move to Switzerland permanently. The strategy works for the UK and other EU countries. https://www.freemovement.org.uk/suri...gration-route/ ) But see this thread: Non EU wife entering on Schengen visa refused permit by Bern commune. Help needed pls