My first thought of what's missing is a good solid bouncy syncopated timpani + double bass strings drone/pulse on low D. And if you fill that in, some variations and flourishes will come to mind with cellos holding a sonorous counter harmony, and maybe if you want, some higher pitched rhythmic stuff like a subtle snare drum or very *soft* suspended cymbal swells.
Also, I think somewhere in the middle where you'd like to make the phrasing feel like it steps up in intensity, but not really move forward yet, that would be a great place to put a high violins sweet sustain on the tonic, maybe doubled in octaves.
Also, this clip is too short to really say if anything is "missing". This could be a great intro or exposition to a repeated section that adds melody on top of the same repeated texture, and that could then develop further. So thinking that this will fit in some larger context, it might be just fine.
A lot of other nuances I think minor changes might bring out the character of this a lot more. (1) I think the swells in the horns are slightly too loud compared to the rest of the textures, the woodwinds and strings get masked and sound weak. (2) Also I feel the tonal bass elements are either missing or a bit too quiet - it feels like you may have mixed on headphones that have good bass, and don't feel it's missing in your listening setup? (3) woodwind runs are a great touch, but I think you may want to program them to be slightly more messy, if possible?. (4) Choir sounds awkwardly hidden and I only hear one choir line in mid-range sopranos, it feels like it would be a beautiful sprinkle, but kinda wish it was at least doubled in octaves, or maybe doubled with altos harmonically. It might be nice to hear if there are syllable chords in the choir. (5) Somewhere in the middle, I felt the rhythm got too abstract and I lost track of where the beats are. I think it may have something to do with the misalignment between just a few too many instruments (I know it helps make performance sound more authentic, but in this case the beat got lost too).
Finally, just to be clear, the reason I have so many thoughts about it in the first place is because the basic premise of your clip was actually pretty great and interesting. So yes, it's sounding really interesting already.