I think adding a SQL format make sense
In conjunction with the other formats that already exist then you can get
Totext( nil, Date.FormatStyles.SQL, Date.FormatStyles.SQL ) => equivalent to sqldatetime
Totext( nil, Date.FormatStyles.SQL, Date.FormatStyles.None ) => equivalent to sqldate
Totext( nil, Date.FormatStyles.None, Date.FormatStyles.SQL ) => there's no current equivalent
Totext( nil, Date.FormatStyles.None, Date.FormatStyles.None ) => an empty text (might as well)
And of course you can always add a locale & get whatever locale savviness you need + whatever other formats there are
You would end up with a lot more flexibility in the long run