SQL Express feature request: running databases in memory

While I like this syntax of SQL Express connection strings:

Server=.\SQLExpress;AttachDbFilename=c:\mydbfile.mdf;Database=db; Trusted_Connection=Yes;

it still doesn’t solve my problem of running integration tests quickly. One option to improve the speed would be to have the database file on a RAM Disk but that is not always possible.

This would be way better:

Server=.\SQLExpress;Database=db; InMemory=Yes; Trusted_Connection=Yes;

Microsoft, when can we have something like this?