The new types [date], [datetime2], and [datetimeoffset] interpret the date literal 'YYYY-AA-BB' as 'year-month-day' regardless of regional or dateformat setting. This is great.
The problem is that [datetime] and [smalldatetime] have always behaved differently, and it appears that unfortunate behavior will be preserved (to provide backward compatibility).
This has the potential to create a lot of confusion. More people will adopt 'YYYY-MM-DD' as a safe format (which it should be, and which it is for the new types), so more people will accidentally use it where it is not safe: [datetime] and [smalldatetime].
I suggest eliminating the 'YYYY-DD-MM' interpretation altogether in Katmai, including for the existing types, and allowing it only for compatibility settings 90 and earlier--if at all.