Lottery system isn't coming till 6.1. Bit early to be worrying about it.

The most likely scenario though is exactly how it sounds. Pay the placard price for the plot you want, your name gets put into a hat and one gets picked after the time expires. Those who didn't get picked would hopefully get refunded the gil they put in. I also would have absolutely no hope in them making it impossible for people with multi-accounts/bots to participate. I fully expect the black market to continue to thrive as well.

In short: prepare for placard camping without the camping and add in 2-5x the amount of people you usually see unless they somehow cap the amount of people who can participate at one time. Prepare for screaming from lots of people if that's the case though.