Frankly, and I know I'm in the minority here, but most long-form musical works are simply vanity projects in an era where rich people no longer pay you to compose them.
I do not know that I have ever listened to any symphony in its entirety, in a single sitting, no matter how good it is. Honestly, most pieces of music longer than 5 minutes really have no business being that long, and starts to either descend into an unnecessary amount of variations and repetition, or may as well be multiple pieces.
Elvis had over 20 #1 hits and I don't think any of them were longer than 3 minutes. This was in the '50s and '60s, when we are told people had longer attention spans. I feel there is an important thing to learn there.
Most people here don't seem to be film composers or TV, but rather aspiring concert composers (at least from what I've noticed) and thus they don't really realize just how much story can be told in 1-2 minutes. In most cases, that is plenty long enough to say what you want to musically, in one coherent idea.
So in short: I don't have any plans of writing a symphony. Right now, I'm putting the finishing touches on an album of adventure orchestral music for TV. The company requires at least 10 tracks, but if I'm being honest, I do feel like I said what needed to be in 8.