considered slightly dubious at the top level but might work as one of the less sound surprise openings out there.

Yes, you can transpose from the Dutch:

1.d4 f5

2.d5 c5

It's also played by Dutch players.  I have seen a game where Danielsen played this, with a variant of the Leningrad Dutch.  You see that the long diagonal is ripe for the king-bishop at g7 to shoot across!

Never seen anything like this.

weird! cool. nice!

A strange game. The only winning move is not to play.

(well, for Black :-D)