Beat me to it... no changes, no refunds, no seat assignments.
You know what though, if DL wants to do this I have no problems, as it'll free up more seats for the rest of us to select... as long as it remains restricted to this lowest fare class and there is no creep into other fares.
I also saw on the booking page a banner for:
EASE INTO AN ECONOMY FARE
Add more convenience
Select your seat in advance
Change flights when plans change
Trade up to Economy Class for only $6.00 more per person each way
Includes taxes & fees