I had read about this new freestyle, but hadn't seen it before - it really breaks some new ground! This is the first freestyle I've seen (doesn't mean there aren't more out there, but the first one I've seen at FEI for sure) that uses all vocal music (which I liked a lot).
I would guess there is no rule against vocal music, but I seem to recall whispering and comment when people have used even "la la la's" (like Anky did in her hum along music).
The only drawback I see is that it is very, very obvious when the music changes and there is no transitional segment - it's just boom, a new song. That happens in other peoples' non-vocal kurs and depending on the particular selections, it can be very obvious as well, but I think the completely different segments are even a bit more apparent with the vocals. And I think the only way you could completely avoid the issue is to pay someone a zillion $$$ to compose a custom piece of music.
Anyone else notice this?
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"If I am fool, it is, at least, a doubting one; and I envy no one the certainty of his self-approved wisdom." Byron