Ken, don't stay away. Not a problem if once folks don't respond the way you expected. Not an issue at all.
We aren't all equal, and it's as valid to disagree as it is to agree. My $0.02, anyway.
As for increased participation:
I wish I had great ideas. But I've long ago learned that folks are what they are.
With the world being the fleeting short term thing it is nowadays, I can understand many not having the time to put in something within the MSA timeframe.
On the other hand, increasing the timeframe will not improve the variety, and that will for sure kill it.
Maybe have more than one subject for each assignment? That will make things flexible for all and easier to enter.
As well, open up for older images. It's not always possible to go out and shoot a particular subject in a timeframe.
More than one assignment theme for each MSA would perhaps make it easier to find a match?
Just an idea. What say you?