Thye main problem with repurposeing the QS-1 is that it's impossible to change the lettering on the function switch to reflect what the built in SM is doing.I have a QS-1 and I did like its looks and sound even though it wasn't the bigger brother models. Of course being a kid of the 70's I love the meters. I have wondered if I found one cheap and not worth restoring if I could retrofit an SM into it and still use the original meters and switches....
Another control center project I did used a QS-500:
When you pull out all the rear ch power amps there's plenty of room to work. Also the top 1/2 plastic faceplate can be replaced with a blank one, and use Letraset presstype to redo the functiom names. In my case I didn't have any internal decoding so the function switch was made to read: QS (QSD-1), SQ (FosgateTate),
etc. The SM would not be a good candidate for this because there is a separate front panel sub-board connected by a ribbon cable to the main board. Then also, what do you do with all those output level controls?
However if you could find a Photolume QS decoder board as @par4ken & I have talked about, it would be a great fit. But then If I remember right you already have a bunch of good toys like QSD-1, QSD-2, etc. Not sure if you would find much of an improvement over that.