Eric Schiller's Gambit Chess Openings (2002) updates DDG analysis started in Unorthodox Chess Openings (1998). Unfortunately, he still covers only one deep line in the Keres Variation: 1.e4 e6 2.d4 d5 3.c4 dxe4 4.Nc3 Nf6 5.f3 c5 6.d5 exd5 7.cxd5 exf3 8.Nxf3 Bd6 9.Bb5+ Nbd7 10.O-O O-O 11.Bg5 h6 12.Bh4.
Acknowledging that his previous recommendation 12...a6 13.Bxd7 Bxd7 14.Ne4 Bf4 is spoiled by 15.Nfd2!, as revealed by DDG News 1/1999, he recommends now 12...Re8 13.Nd2 g5 14.Nc4 Bxh2+ 15.Kxh2 gxh4 16.Qf3 Rf8, which is "unclear and can lead to a draw": 17.Qf4 h5 18.Qg5+ Kh7 19.Qf5+.
Instead of 18.Qg5+, White can improve with 18.Bxd7 Nxd7 19.Qh6, threatening Rf5 or Ne4:
Note that 14...Bf8 15.Qf3!! was played in a spectacular game Heikkinen - Rebel Decade, 1996.