They could be used to interdict smugglers coming in from Baja, the Gulf or the Keys; to chase down pirates in the Red Sea, and/or to escort in or to patrol in short to medium length commercial channels e.g. from India to the Suez, or from the Suez to Sweden. The stealth part I don’t really figure as critical but maybe it’s got a future in the front line of a sea-based landing, or maybe it is just one version proof of concept for future, larger ship with a different purpose.
A stretched-Visby class ship would have been perfect for the littoral role which the USN is buying the hugely expensive LCS, which is currently plagued by performance and equipment issues.