Did he finally go mad ?

This afternoon, I got to talk to one of my BDG buddies. We went through my sunday game which I started off as follows :

1.d4 Nf6 2.f3
Inviting ( no, begging !! )  my opponent to go into a Blackmar Diemer... But alas, my opponent wisely thanked for the invitation.
2...g6
I played the normal (??) move here.
3.e4

"Stop right here", my chess buddy said. "Why not consider 3.g4 ?? You will play it lateron anyway - why not play it right now ?"

At first, I could not believe my eyes. But my friend was right - what is keeping me from this adacious move ? It is a legal move after all !

Let's check out the natural line 3...Bg7 4.h4 (diagram)

Now believe me or not, my Stockfish chess assistant indicates that only one move offers black an advantage. Can you find it ? I bet you wont.

Let's check out a few alternatives

a/ 4...d6 ( the normal Pirc-ish move ) 5.h5

and now black only has 5...gxh5 6.g5 Nfd7 7.Rh5 leading to equality.

b/ 4...c5 5.d5

\
...b1/ 5...e6 6.e4 exd5 7.e5 (?!)
......b1a/ 7...Qe7 8.Qe2 Ng8 9.Nc3 (=)
......b1b/ 7...Ng8 8.Nc3 d4 9.Nd5 Ne7 10.Nf6+ (=+) with a complicated game
...b2/ 5...d6 6.e4 (=)
...b3/ 5...Qa5+ 6.Kf2 !!!! (=)
...b4/ 5...0-0 6.h5 (=)

c/ 4...d5 5.h5

...c1/ 5...Qd6 6.Nh3 (=)
...c2/ 5...c5 6.h6 Bf8 7.e3 (=)
...c3/ 5...gxh5 6.g5
......c3a/ 6...Nfd7 7.Nh3 (=)
......c3b/ 6...Ng8 7.Nh3 (=)

I am sure you will tell me this opening does not make sense. But hey, remember Diemer's "immortal" game against Trommsdorf in 1975 in Bagnieux, France. That game stood the test of time - and I am sure, most of our games wont be remembered in 50 years time...