Rather than giving the users a big list of different date formats to choose from, allow the user to construct their own format with syntax of the incoming date that they are dealing with.
Currently I need to do a string function moving dates around to match a predefined syntax...
We've gotten this request quite frequently and have never implemented it because there's a pretty easy workaround (using the DateTimeParse function or DateTimeFormat function in the Formula tool).
However, this is clearly a popular request and we're now reviewing it to see if we can get it into a future release.