SDP would be good, if not better than NDP. More fitting and more telling than a name like NDP which can apply to any type of party, from fascist to Trot.
Progressive? No. There can only be one Progressive Party, the rural 1920s Progressives.
Well, they could change the name to the New Progressive Party. 
What about Democratic Progressive Party (DPP - also the name of a Taiwanese Party)
I think the added joke was that the New Progressive Party is the pro-statehood party in Puerto Rico, thus implying that a Canadian party by the same name would advocate annexation by the US. Or maybe I was reading too much into it.
I don't have an objection to "New Democratic Party" as a name. Political party names are rarely descriptive of their philosophies or natures, anyway. Certainly it isn't true almost anywhere outside of Europe. I know Canadians secretly want to be Europeans, but...
If they have to change the name, become the Social Democrats. Any other name change would be overtly cynical.
