Seems to me that the system in the Turtledove selection polls works well enough without any voting restrictions. I think having restrictions like that would be more trouble than they're worth.I actually think this sounds generally like a good idea. Approval voting is used for the Turtledove selection polls, and it works quite well there. Or maybe we could have a poll with approval voting, but with a limit on the number of votes each user can cast (of course, then we would have to do a visible vote poll to ensure that no one casts too many votes).
Here you go.No botes for me?
...I couldn't resist.