this has been suggested before. I agree but in that diagram position its easy to conditional-move both lines; the feature would be more useful in positions like this.
Conditional moves - how about introducing a "IF ANY" move feature
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Erik seemed to be in favour of it ... 3 years ago ...
conditional-move---dont-care-option
and made encouraging noises when this was raised 2 years ago ...
conditional-moves-in-online-chess
potential-new-conditional-move-features
(This was an interesting discussion ... conditional-moves9).
For example in this position:
Whatever move Black makes white will move the queen to a2 for checkmate.