The Form 8938 thresholds are fixed regulatory amounts and they depend on two things: filing status and where you live. They are not indexed for inflation. For a taxpayer living in the United States, Form 8938 is required if specified foreign financial assets exceed $50,000 on the last day of the year or $75,000 at any time during the year for a single filer, and $100,000 year-end or $150,000 at any time for a married couple filing jointly. For a taxpayer whose tax home is abroad, the thresholds quadruple: $200,000 year-end or $300,000 at any time single, and $400,000 year-end or $600,000 at any time for a joint return. Crossing the threshold triggers the report; it does not by itself create any tax.
What Form 8938 covers is broader than a bank account. Specified foreign financial assets include foreign bank and brokerage accounts, but also foreign stock or securities not held in an account, interests in foreign entities, and certain foreign financial instruments and contracts. This is wider than the FBAR's account-based scope, which is one of the reasons the two reports do not substitute for each other. Failing to file Form 8938 when required carries its own penalties, beginning with a substantial flat penalty and rising if the failure continues after the IRS gives notice, and the statute of limitations on the whole return can stay open where the form is missing.
The institutional side reshaped banking for Americans abroad. To avoid the 30 percent withholding, most of the world's financial institutions agreed to report US account holders, either directly or through intergovernmental agreements their home countries signed with the United States. That machinery is effective at surfacing accounts, but it also made US customers expensive to serve, and some foreign banks responded by declining to open or maintain accounts for US citizens rather than take on the reporting burden. An "accidental American" who has never lived in the United States can find a local bank asking for a US taxpayer identification number because of this rule.
FATCA is why the "hidden offshore account" is largely a thing of the past for ordinary savers. The combination of taxpayer reporting and institutional reporting means the government generally learns about a foreign account through at least one channel. Holding money abroad remains perfectly legal; the change FATCA made is that not reporting it is much harder to get away with.