I would then sit on a single 980Ti until either AMD stun us with Navi or 7nm Nvidia cards roll around (or at least until I can finally pick up a 1080Ti for around £300-350 if the 7nm pricing disappoints).
This is essentially my planned course of action, and the only thing I could recommend to anyone running a 980ti right now. It still holds its own very well as a single card (I get roughly 70 to 80fps in bf5 with only 2 settings below max at 1440p). As you say, multi gpu is just pants, and it has been for a long time. Gone are the halcyon days of xfire 6950s actually working really well, and now it's just frustration as one gpu becomes an expensive paperweight in most titles.