Maybe a small programming idea, in lieu of a MultiPV, Rebel always championed the exclusion search in the past (less difficult than Multi PV mode which is tricky to get it somewhat right) and since on my computer at least CS Tal and Rebel are limited to two threads anyway, but are already very strong with one, maybe it would be nice if a second thread could do an exclusion search, maybe automatically changing when the best move in the main thread changes, of everything except the strongest move at the moment. So the search becomes quite a bit wider, when using two threads instead of one. I think Rebel and CS Tal already do this to some extent (search the second best move deeper than other moves)?
For instance in the position from Jouni in Talkchess,
https://talkchess.com/forum3/viewtopic.php?f=2&t=82619, Caruana - Carlsen, Rebel EAS after nine seconds can see 23. g2-g4 is good but then loses it again for a Rook move (which may also win, I do not know, but in Multi PV 23.g4 is stronger);
21/35 0:07 +2.85++ 23.Tad1 (3.232.037)
21/41 0:09 +2.78++ 23.g4 (4.131.479)
21/38 0:11 +2.72++ 23.g4 (4.513.484)
21/36 0:11 +2.64 23.g4 Lg6 24.Tad1 Ld6 25.Tfe1 c4
26.Pxc4 Te8 27.Txe8+ Lxe8 28.Pxd6 Dxd6
29.De4 Tc8 30.Df5 Ld7 31.Dxg5+ Dg6
32.Dxg6+ hxg6 33.g5 Kf7 34.Td4 Tc5
35.Kf2 Ke7 36.Te4+ (4.549.702)
22/44 0:18 +2.34 23.Tae1 Lf6 24.h4 gxh4 25.Dxf4 Lxc3
26.bxc3 Lg6 27.Dh2 Dg5 28.Pd7 Txf1+
29.Txf1 Tc8 30.Dd6 h3 31.De6+ Kg7
32.Dxh3 Te8 33.c4 Dd2 34.Kh2 Dd4
35.Dg3 Dxc4 36.Tf3 (6.127.784)
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