Replying to the whole voting thing, I think that's kind of destroying the whole purpose of a "just get out there and do it" thing that this would be. Sure, I wouldn't mind where people could rate their favorite ones and write reviews or whatever, but there definately wouldn't be any sort of winner, except maybe some awards for "Best Setting" or "Most Creative Puzzle" or whatever, sort of a long the lines of the XYZZY Awards, except strictly to the NaIfProMo.
I don't think it's a good idea to push for the games to be uploaded and made public during/directly after the month. I just did NaNoWriMo for the first time this year (and won - just) and there's no way I'm showing anyone the horrendous mess of text I finished up with until I've done a LOT of editing.
Given, a short IF work can be written fairly well in a month (wasn't that how long J Robinson Wheeler took over Being Andrew Plotkin?). All the same, I wouldn't be keen on uploading my game anywhere until I had finished and had some beta-testing done. I certainly wouldn't want anyone giving me feedback in the middle of the month - the temptation to go back and edit instead of pushing on and finishing first would be overwhelming.
One of the reasons NaNoWriMo is so successful is simply that everyone who gives it a go is a winner. Even if you don't get to 50,000 words and don't get your nice winner's certificate and icons, it's still really cool that you gave it a go and wrote something instead of continuing to say, "One day, I'll write a novel..." Introducing the idea of awards would turn it into just another comp, with the addition of a weird rule that your game must be written in a month.
Don't get me wrong, I do think NaIfProMo is a cool idea. I'd definitely be interested in doing it. May sounds like a pretty good month - it gives some space after Spring Thing (not much, but you can't push it back too far - most people don't do ST anyway) and plenty of time before the IFcomp. (People might even want to enter their NaIfProMo games into the IFcomp - they'd have plenty of time to tidy them up. Another reason not to push people to make their NaIfProMo games public if they don't want to.)
The main question is - how do you establish the IF equivalent of 50,000 words? I admit to having no real ideas. I'm a little dubious about the idea of a minimum-length walkthrough. It would, of course, be possible for an author to implement one path through a game and nothing that deviates from this path. Though I suppose this would be the NaIfProMo equivalent of padding - doing whatever you can within the rules, no matter how dishonourable, in order to make your target. (Yes, I padded my novel too. Majorly.)