ranjit I think it's more of a "talent" than growing up monolingual or bilingual. Some people seem to be better at mimicking sounds. I've seen a few monolingual who can do this, and plenty of multilinguals who can not.
Definitely some people have more facility with spoken language than others, whether mono- or multi-lingual. What I'm trying to get at is whether some languages, when learned early (or ever; I'm not clear on how important timing is), make it easier for most speakers to learn other languages in the future. So, do people who are mono-lingual in my native language thereby have an advantage in the future if they want to learn other languages? Do Americans who are mono-lingual in English have a relative disadvantage in trying to learn other languages?
Bringing it back to the piano - does playing a lot of classical pieces in the beginning (or doing whatever "classical piano training" constitutes) set up players physically (in their fingers, and in some ways their ears) to more easily move into non-classical music, compared to the reverse direction? Does the classical training set up a physical and/or mental architecture that provides a broader base for piano playing than non-classical training that avoids playing classical piano pieces? Again, I'm not suggesting that classical technique or training is all-encompassing. When I watch some jazz players work together, or hear how someone like HeartKeys works, I sometimes feel like I'm watching humans who have the ability to fly. No wings, no jet packs; they just have an extra ability to fly that ordinary humans don't have. It's something like a miracle to me. So I'm very clear that there are some aspects of the non-classical world which are completely orthogonal to the classical world.
I don't know whether broad generalizations are possible. But for someone like me, it's very clear that it's important to wire in balanced physical development on the left and right sides as soon as possible. (I am very right-side dominant, and except for my arms and hands, I'm permanently physically askew because my parents allowed me to develop in such an unbalanced way. It's had long-term knock-on effects that I'll struggle with for the rest of my life.) I don't know whether a focus on even left/right-hand development is that important for most people, but what I have noted is that in both karate and horseback riding, there's a deliberate and intense focus on trying to make sure that the left- and right-hand sides develop equally from the beginning. There are several horses at the stables that are like me - scoliosis, a tendency to bow out when we should be moving in a straight line - and they have to have extra training throughout the week to try to keep them as muscularly even as possible. My son rides one of these horses, and the children's instructor has made the point many times that if they don't want to "be like Jersey", they cannot allow themselves to favor one side over the over. I wonder if starting the piano with a method (or initially primarily playing pieces) that requires much more dexterity from the right hand compared to the left is essentially wiring in a physical imbalance that cannot be easily, or perhaps ever, overcome.
As an aside - if you're looking at bilingual people, I think it's important to also consider which languages they know. My sense is that English/ Spanish and English/Italian doesn't require the same breadth of mental architecture as English/Korean, English/Japanese, or English/German does, because the phonemes in Spanish and Italian are so close to English, and the grammatical structures are so similar as well.