Yes Dann, you're right. I badly explained myself : my idea is not really nullmove but only a nullmove for the opponent. As if you can play 3 moves and not the opponent. Maybe there is another name for this.
I don't understand how this will help.
Everything will look winning.
The reason null move works so well is that most moves are bad. A move that is worse than doing nothing does not need to be explored as carefully most of the time. But test suites often turn this sort of idea on it's head. That is the reason that they are fun. They usually involve a surprising sequen...
I think the idea would be better for quiet moves than for test problems.
Lots of test problems involve either sacrifices or zugzwang positions. Both of these are problematic for null moves.
Often, giving up a piece looks worse than a pass.
And when you are zugzwang, you don't want to pass.
I don't think it will help a lot in general because at the start of the game of chess, the good moves are well known, and chess engines already do a lot of pruning in general searching (e.g. the branching factor for Stockfish and other very strong engines is about 1.5). But it could not hurt to try ...