Wayne, the 13-18 bracket would actually allow for some form of anti-tanking measure to be brought in. Wins in those final five rounds would help a team move up the draft order. I don't know the exact mechanism for how that would look, but it wouldn't be too difficult to come up with something that significantly reduces the risk of tanking.
Yeah spot on Chuznut, I can't see a side intentionally avoiding the top six.
Andy_Roo, yep that's also an issue. In some ways it would be like finals. The AFL would probably need to book accomodation in each city in advance and the same arrangements as finals used for travel. Potentially you'd also have a bye weekend after Round 17 to sort the fixture out etc. Call it 'Community Footy Weekend' or what have you.