As you know, I‘m in the same boat. If we really see a delivery of the 8K to us midrange number backers in say October, and the 1180 releases end of August, it would mean we‘d have to wait for something like 6 months.
I believe you need to consider buying the 1180 and upgrading to the 1180Ti later on, when it becomes available. You will probably loose 200-300 bucks compared to the 1180Ti only scenario, so you have to figure out if you are okay to pay roughly 50,- per months to fully enjoy your 8K. I must admit I am really contemplating it. But I will surely wait until I receive my 8K and have checked that it works. At that point in time I will know how long the anticipated time till availability of the 1180Ti is, what the general experience with the 8K is, and then make the call. It should only take a few days till the 1180 would be delivered so I can wait for that. And possibly we already would have alternatives to the founders edition (same goes for the Ti, if that is supposed to be the high-end GPU for me for some time, I‘d better wait for the OC versions).