I originally said 2020 and I'm sticking by that despite no actual evidence either way. If it was just a facelift in 2016 I might expect an updated model sooner but there were enough interior changes as well as the 8 speed transmission that I think Toyota is going to try and milk the $ they put into the redesign for a few more years, possibly even using some of the interior redesign in the next version.
That said Kurt seems to have the most inside info. If I was a betting man I'd put my $ on the biggest change being a twin turbo V6, similar to what Ford did with the F-150. Not because the LC is trying to compete with the F-150, but because that's ultimately the direction the manufacturers are going to improve mileage.