GF is a GF. It might not get the 99-100k figure but it'll be a sell-out and end up around 95-97k I suspect.
Ratings might also be worth watching. Grand Finals from 2003-2016 highest ratings
1. Sydney v West Coast 2005, 3,386,000
2. Sydney v Hawthorn 2012, 3,196,000
3. Sydney v West Coast 2006, 3,145,000
4. Sydney v Western Bulldogs 2016, 3,030,000
5. Brisbane v Collingwood 2003, 2,965,600
6. Geelong v St Kilda 2009, 2,878,000
7. Sydney v Hawthorn 2014, 2,813,000
8. Port Adelaide v Brisbane 2004, 2,796,000
9. Collingwood v St Kilda 2010 Game 1, 2,768,000
10. Hawthorn v Fremantle 2013, 2,717,000
11. Collingwood v St Kilda 2010 Game 2, 2,687,000
12. Geelong v Collingwood 2011, 2,641,000
13. Hawthorn v West Coast 2015, 2,640,000
14. Geelong v Port Adelaide 2007, 2,563,000
15. Hawthorn v Geelong 2008, 2,491,000
5 of the top 7 rating games according to what I found on wiki have been Sydney Grand Finals. We might have 4-8k less at the ground (probably just less corporates anyway, so who cares) but I very much doubt there'll be a whole lot less interest than normal, it'll reach heavily into Sydney. They as a city, just like with rugby and A-league, have much better 'success' with ratings than attendances. I expect it'd probably fall short of the 2016 GF but be around the 3 million mark.
If it's a Richmond GF then the ticket rush will be crazy but I doubt it'd destroy those numbers ratings-wise.