The outer mount has room for a 3-slot cooler - but it's quite close to the glass. An air cooled GPU could have issues with cooling in this mounting position but a liquid cooled GPU will be just fine.
You also have room behind the GPU for Add In Cards ... and the GPU will do a good job of 'hiding' them too. You'd have to take care to route the PCIe riser cable over the AIC and remove the GPU if you want to add/remove most expansion cards
You even have enough space, if you want, to have a second GPU mounted vertically - one in the outer mount and one on one of the inner mounts. However, you'd have a challenge or two routing the PCIe extensions so it's probably not a very good idea to do that.