I have run two Kepler GTX Titans and a GTX690 in this machine ok for a few years before I went water on the Titans.  I would think the EVGA GTX 1080Ti's would be fine with those larger more open coolers in there with a GTX Titan X at top.  It wouldn't be much more than 30 minute down time to rearrange to have the AC unit more directed to wards the system anyways if cooling gets that bad.  By the time I am able to scale to a dedicated machine I was planning on doing an open rack design on a wire shelf and using the crap ton of fans I have collected over the years to zip tie and direct airflow.
 
The wife's computer with three GTX960's

 
My current rig with the GTX Titan X(p) and GTX 690(I run four monitors, three of which are very picky with adapters so needed a card w/3 DVI)

 
I used to have a WC setup that looked like this but a component failed and I didn't want to wait on the hassle of getting it replaced so I pulled it all out and went AIO.  Since I replaced my two Titans with the Titan X there was not really a need to reinvest in a loop.

Before the WC loop the cards were configured the same with stock coolers but it ran fine.

 
 
If I were looking into making a truly dedicated monster folder I think I already have the base for one.  That ASUS ESC4000 G2 box that I rebuilt for less than $700 from ebay parts is basically a GPU monster machine crammed into a 2U server box.  I slapped in two 8 core Xeons and 32gb of ram but have yet to put it to any real use.  80-PCIe lanes up for grabs though.  I would have to experiment with it but it may be possible to run a supplementary PSU and drive up to 8 cards in a BTC Miner rack with PCIe extensions off of this thing.  If that works then the $700 invested may actually pay out and I wouldn't have to pay for hardware beyond a PSU and GPUs w/ extensions.
 



 
 

Chris21010
i have yet to re-advise going that route as i currently have 110K FLDC in limbo until polo fixes their wallets which have been down for a week... yes you may save some in fee's but at least you have access to it and not be at the whim of a 3rd party to update their wallets.

 That's a Polo issue - among MANY OTHER issues I had with them in the roughly 2 months I tried to use their exchange, only to see issue after problem after trouble.
 Stay away from Polo, they MAY have been good at one time but they are total garbage now.
 
 4 card rigs on air for non-riser rigs are ... problematical on air, especially with higher-power cards like the 1080 and 1080ti and any Titan, and marginal at best with the 1070.
 Blower cards seem to work a lot better in that tight of a setup, but even then they're still going to run warm due to intake restrictions.
 
 That's why I've settled on my 3-card rigs, one a "shortie", and constantly curse the moron MB makers that insist on doing 2-5-7 spacing on 3-card motherboards....