I first became aware of this line over a decade ago playing in opens in Spain, where I knew it as "the Vallejo plan". I soon started playing it enthusiastically myself. 

In a way therefore I was disappointed when GM Markus Ragger published a rather good article on it in Yearbook 124! He explains things very clearly and at some length and I think one could certainly start playing it for Black just on that basis. Ragger also covers White playing Nf3, instead of e3 and Nge2.

One odd thing is that even if White is able to play the logical e3, Nge2 and d4, Black's 'Italian' bishop still often plays an important role.

In my experience (both over the board and online), although I think White should be OK, especially if he defers castling, even then the positions arising can become very sharp and unbalanced and probably not to the taste of most 1 c4 players who favour an early g3 set-up.

It seems that Sielecki advocates 7.Rb1 h5 8.h4 Nf6 9.b4 Be6 10.Nd5 Rb8 11.a4, Petursson,M (2520) - Fedorchuk,S (2635) Berlin 2015.

RoleyPoley wrote on 03/22/21 at 11:30:26:

I don't think it's the same line. His comments resemble the variations that Williams and Palliser give.

Checking the 'usual culprit' for new ideas these days - 6.. h5!? is LC0's top choice on move 6 Maybe modern SF variants too, haven't checked.

After 6.. Ba7 7 d4 it doesn't even think that its that close - 7.. h5 a definitely better move than anything else. 
(~45% for black vs 40% otherwise.).

That will explain a continued stream of modern players playing it, but not games back in 2017 but then Anand would tend to be head of opening trends  

It is a rather thematic idea once white has gone Nge2.

There is a line that is surprisingly common online, and scores extremely well in GM play, yet as best I can tell does not receive coverage from either Watson (Mastering the Chess Openings, Vol. 3) nor Kosten in The Dynamic English.  Perhaps I am just missing it?  The line is where Black plays e5+d6+Nf6+Bc5, immediately pulls the bishop back to a7, and then lunges with the h-pawn.

1. c4 e5 2. g3 Nc6 3. Bg2 Bc5 4. Nc3 d6 5. e3 a6 6. Nge2 Ba7 with 7...h5 on the next move regardless of 7. d4 or 7. 0-0

This has been played in tons of master-level games on lichess -- in fact 3...Bc5 is more common than the kingside fianchetto and equal in popularity to the Reversed Grand Prix Attack -- as well as a couple dozen GM games.  The most high-level encounter was Anand playing it at the World Cup a couple years ago:

[Event "FIDE World Cup"]
[Site "Tbilisi"]
[Date "2017.09.07"]
[Round "2.2"]
[White "Kovalyov, Anton"]
[Black "Anand, Viswanathan"]
[Result "1/2-1/2"]

1. c4 e5 2. g3 Bc5 3. Nc3 Nc6 4. Bg2 a6 5. e3 d6 6. Nge2 h5 7. d4 Ba7 8. dxe5
dxe5 9. Bxc6+ bxc6 10. Qxd8+ Kxd8 11. h3 Nf6 12. b3 Be6 13. Ba3 Kc8 14. Na4 Ne4
15. Nec3 Ng5 16. h4 Nf3+ 17. Kf1 Kb7 18. Kg2 Bg4 19. Ne4 Rhd8 20. Be7 Re8 21.
Bb4 c5 22. Bc3 f6 23. Naxc5+ Bxc5 24. Nxc5+ Ka7 25. b4 g5 26. hxg5 Nxg5 27. f4
exf4 28. gxf4 Rxe3 29. Bd4 Re2+ 30. Kf1 Nh7 31. Re1 Rxe1+ 1/2-1/2

Black has scored exceptionally well in this line.  In particular, if White plays 7. 0-0 then Black's score in Megabase is 63% after 7...h5.

My question is, where is everyone finding this?  Who is telling everybody to play it?  And where, if anywhere, is there coverage for White?