Is is feasible to drain it now, do all the work this fall, and have a pond ready to be stocked by next spring?
Unlikely, as mentioned you would have to wait for the muck to dry to move it, and that can take quite a while if rain hits or you have a spring. If you are unlucky you can get a bad drought which oddly helped a lot of fisheries out in the past few years, allowing renovations and expansions.
Based on what you observe with a good 10' or more bottom, it may not be worth it to drain. You may have a lot of muck, but the pond may have also been really deep to begin with. Adding aeration may also help break some muck down over time as well. This may release some nutrients into the water column though...
Based on your observations of panfish spawning, I am guessing you have larger bass somewhere in there, perhaps a bit hook shy?
