Your idea is more interesting)))
And I want to say thank you. Your game Flying Aces help me to find solution to work with sound loops in Godot.
You use a creative hack, in order to engine sound loops. I tryed the same, but this hack has own limitations. And than I understand, what was wrong. Whan game starts, Godot drops the set_loop_format option to 0 (do not know why). Then I just neet to set it in _ready to
get_node("SamplePlayer").get_sample_library().get_sample("engine").set_loop_format(1)