Gardener

It's likely to be rejected, yes, but that doesn't mean you shouldn't do it. It can't hurt you, and who knows, if the person in charge really likes your piece they just might do it. But you might consider first which orchestra to approach. Not all are equally fond of taking risks or supporting young composers. Generally, the bigger they are and the more they depend on making money, the less likely they'll do it.

But sometimes you just need the courage to do something a bit crazy.

To get back again on the main topic, when it comes to composing I think for most composers it's some sort of compromise anyways. On one extreme, you could just write solos for the most easily available instruments, not too hard but still good enough for showing off the abilities of the player, not too long, etc. It will be rather easy to get people to play your pieces like this, but the question is whether with all these restrictions you can still truly do what you want, musically, or whether you're just prostituting yourself. On the other extreme you might write music that conforms entirely to your musical visions, but which is unplayably hard, requires huge quantities of rare instruments and lasts ten hours, but you probably will never actually hear your music nor will anybody else.

Usually it's something in the middle, sometimes leaning more to one, or the other side. You might for example write with the definite intention of getting it performed, but still require good performers, use uncommon techniques and will require time, effort and money to perform. Or you might write without the definite intention of getting a performance, but still write everything so it could be performed, if someone was willing to do it. Personally, I'm facing the question of practicability versus "musical vision" quite often. For example, currently, while working on my piece for three pianos, I'm trying to decide whether to retune some select strings of the pianos. On one hand I'd really like to do it and I could better put into effect what I want, but on the other hand I don't really need it, and it will make getting a performance quite a bit harder (many institutions, including my conservatory, are rather strict about preparing their pianos and they usually only have a single one that you can prepare/retune). A compromise would be just requiring a few keys of a single piano to be retuned. And at the same time I'm pondering whether I need a conductor for the piece or not, and if I want to do it without one, how I could simplify the rhythmic organisation to make the coordination possible.