Just a head's up. I randomly checked the Downtown Indy Hilton's website and saw that you can already reserve rooms there for the 2018 GenCon dates. In the past, they didn't seem to open reservations for those dates until January or later.
The rooms aren't cheap (out of the housing block), but if you can snag a reservation you can cancel, it's not a bad idea to grab one as a (albeit pricey) back-up downtown hotel room, if you get screwed over on the housing lottery.
Failing to plan is planning to fail, people!